6,103 results
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2. Zombie states for description of structure and dynamics of multi-electron systems.
- Author
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Shalashilin, Dmitrii V.
- Subjects
FERMIONS ,COHERENT states ,QUANTUM theory ,PARTICLES (Nuclear physics) ,ANNIHILATION reactions ,MATHEMATICAL models - Abstract
Canonical Coherent States (CSs) of Harmonic Oscillator have been extensively used as a basis in a number of computational methods of quantum dynamics. However, generalising such techniques for fermionic systems is difficult because Fermionic Coherent States (FCSs) require complicated algebra of Grassmann numbers not well suited for numerical calculations. This paper introduces a coherent antisymmetrised superposition of “dead” and “alive” electronic states called here Zombie State (ZS), which can be used in a manner of FCSs but without Grassmann algebra. Instead, for Zombie States, a very simple sign-changing rule is used in the definition of creation and annihilation operators. Then, calculation of electronic structure Hamiltonian matrix elements between two ZSs becomes very simple and a straightforward technique for time propagation of fermionic wave functions can be developed. By analogy with the existing methods based on Canonical Coherent States of Harmonic Oscillator, fermionic wave functions can be propagated using a set of randomly selected Zombie States as a basis. As a proof of principles, the proposed Coupled Zombie States approach is tested on a simple example showing that the technique is exact. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
3. Reconciling semiclassical and Bohmian mechanics. III. Scattering states for continuous potentials.
- Author
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Trahan, Corey and Poirier, Bill
- Subjects
QUANTUM trajectories ,QUANTUM field theory ,ENERGY levels (Quantum mechanics) ,CHEMICAL decomposition ,SCHRODINGER equation ,PARTICLES (Nuclear physics) ,PHYSICS - Abstract
In a previous paper [B. Poirier, J. Chem. Phys. 121, 4501 (2004)] a unique bipolar decomposition Ψ=Ψ
1 +Ψ2 was presented for stationary bound states Ψ of the one-dimensional Schrödinger equation, such that the components Ψ1 and Ψ2 approach their semiclassical WKB analogs in the large-action limit. The corresponding bipolar quantum trajectories, as defined in the usual Bohmian mechanical formulation, are classical-like and well behaved, even when Ψ has many nodes or is wildly oscillatory. A modification for discontinuous potential stationary scattering states was presented in a second, companion paper [C. Trahan and B. Poirier, J. Chem. Phys.124, 034115 (2006), previous paper], whose generalization for continuous potentials is given here. The result is an exact quantum scattering methodology using classical trajectories. For additional convenience in handling the tunneling case, a constant-velocity-trajectory version is also developed. [ABSTRACT FROM AUTHOR]- Published
- 2006
- Full Text
- View/download PDF
4. Primal quantization postulate for quantum fields.
- Author
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Haase, Richard W.
- Subjects
QUANTUM field theory ,DIRAC equation ,PARTICLES (Nuclear physics) ,NUCLEAR families ,QUANTUM wells ,AXIOMS - Abstract
We formulate a theory of quantum fields underpinned solely by the full geometric algebra structure generated by the vector space of spacetime. A modified dynamical equation of a field with associated background field potentials, distinct from Dirac's equation, is developed and corrects the inertial potential that acts on the field. A discrete wavenumber spectrum with a possible correlation to the mass spectrum of elementary particles is obtained, and explicit expressions are derived. The formulation is mathematically driven and constitutes what we refer to as the primal field quantization postulate. While manifestly a relativistic quantum field theory, our formulation may provide a natural account of mass hierarchy and family generation. A fourth family of elementary particles is predicted, indicating that lepton and quark oscillations across generation members, as well as quantum decay processes and fluctuations, may need modifying. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
5. Analysis of atomic Pauli potentials and their large-Z limit.
- Author
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Redd, Jeremy J. and Cancio, Antonio C.
- Subjects
DENSITY functional theory ,NUCLEAR charge ,PARTICLES (Nuclear physics) ,MATHEMATICAL analysis ,ENERGY density - Abstract
Modeling the Pauli energy, the contribution to the kinetic energy caused by Pauli statistics, without using orbitals is the open problem of orbital-free density functional theory. An important aspect of this problem is correctly reproducing the Pauli potential, the response of the Pauli kinetic energy to a change in density. We analyze the behavior of the Pauli potential of non-relativistic neutral atoms under Lieb–Simon scaling—the process of taking nuclear charge and particle number to infinity, in which the kinetic energy tends to the Thomas–Fermi limit. We do this by mathematical analysis of the near-nuclear region and by calculating the exact orbital-dependent Pauli potential using the approach of Levy and Ouyang for closed-shell atoms out to element Z = 976. In rough analogy to Lieb and Simon's own findings for the charge density, we find that the potential does not converge smoothly to the Thomas–Fermi limit on a point-by-point basis but separates into several distinct regions of behavior. Near the nucleus, the potential approaches a constant given by the difference in energy between the lowest and highest occupied eigenvalues. We discover a transition region in the outer core where the potential deviates unexpectedly and predictably from both the Thomas–Fermi potential and the gradient expansion correction to it. These results may provide insight into the semi-classical description of Pauli statistics and new constraints to aid the improvement of orbital-free density functional theory functionals. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
6. The FADE mass-stat: A technique for inserting or deleting particles in molecular dynamics simulations.
- Author
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Borg, Matthew K., Lockerby, Duncan A., and Reese, Jason M.
- Subjects
PARTICLES (Nuclear physics) ,MOLECULAR dynamics ,CHEMICAL relaxation ,INTERMOLECULAR forces ,ELECTRON relaxation time ,ARBITRARY constants - Abstract
The emergence of new applications of molecular dynamics (MD) simulation calls for the development of mass-statting procedures that insert or delete particles on-the-fly. In this paper we present a new mass-stat which we term FADE, because it gradually "fades-in" (inserts) or "fades-out" (deletes) molecules over a short relaxation period within a MD simulation. FADE applies a time-weighted relaxation to the intermolecular pair forces between the inserting/deleting molecule and any neighbouring molecules. The weighting function we propose in this paper is a piece-wise polynomial that can be described entirely by two parameters: the relaxation time scale and the order of the polynomial. FADE inherently conserves overall system momentum independent of the form of the weighting function. We demonstrate various simulations of insertions of atomic argon, polyatomic TIP4P water, polymer strands, and C
60 Buckminsterfullerene molecules.We propose FADE parameters and a maximum density variation per insertion-instance that restricts spurious potential energy changes entering the system within desired tolerances. We also demonstrate in this paper that FADE compares very well to an existing insertion algorithm called USHER, in terms of accuracy, insertion rate (in dense fluids), and computational efficiency. The USHER algorithm is applicable to monatomic and water molecules only, but we demonstrate that FADE can be generally applied to various forms and sizes of molecules, such as polymeric molecules of long aspect ratio, and spherical carbon fullerenes with hollow interiors. [ABSTRACT FROM AUTHOR]- Published
- 2014
- Full Text
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7. Cherenkov radiation by an electron bunch moving in Hermitian medium.
- Author
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Liu, Shenggang, Zhang, Yaxin, Yan, Yang, Hu, Min, and Zhong, Renbin
- Subjects
CHERENKOV radiation ,PARTICLES (Nuclear physics) ,HERMITIAN structures ,TERAHERTZ technology ,OPTICS - Abstract
Detailed theoretical investigation and computer calculations on Cherenkov radiation (CR) by an electron bunch moving uniformly in Hermitian medium (CRH) with and without absorption are presented in the paper. The theory shows that in the CRH, not only the current density but also the charge density of the particle contribute to the Cherenkov radiation. It has been found that there are two modes in the CRH; in general, only one of them is radiative mode and another one is local field. The frequency area where both of these two modes are radiative modes simultaneously is studied. The comparison of the two modes is given in the paper and the relation of the existence of these two modes is improved. The comparison of the calculations shows that the radiation power of mode “o” is larger than that of mode “e.” It indicates that the group velocity in the CRH is slower than the phase velocity. Detailed computer calculations are given in the paper, and some interesting physical phenomena of CR are revealed. The theory gives a simple physical interpretation of the inner fine structure of the CRH; it is concluded that the mechanism of the appearance of the inner fine structure of CR is that in a dispersive medium the group velocity is less than the phase velocity. Possible applications of this theory are also discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
8. Comparison of density functionals for differences between the high- (5T2g) and low- (1A1g) spin states of iron(II) compounds. IV. Results for the ferrous complexes [Fe(L)(‘NHS4’)].
- Author
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Ganzenmüller, Georg, Berkaïne, Nabil, Fouqueau, Antony, Casida, Mark E., and Reiher, Markus
- Subjects
DENSITY functionals ,IRON ,MOLECULES ,PARTICLES (Nuclear physics) ,FUNCTIONAL analysis ,CALCULUS of variations - Abstract
Previous work testing density functionals for use in calculating high-spin–low-spin energy differences, ΔE
HL , for iron(II) spin-crossover transitions has tended to conclude that only properly reparametrized hybrid functionals can predict ΔEHL since it seems to depend critically on a correct description of the electron pairing energy governed by the exchange term. Exceptions to this rule are the previous three papers (I, II, and III in the present series of papers) where it was found that modern generalized gradient approximations (GGAs) and meta-GGAs could do as well as hybrid functionals, if not better, for this type of problem. In the present paper, we extend these previous studies to five more molecules which are too large to treat with high-quality ab initio calculations, namely, the series [Fe(L)(‘NHS4 ’)], where NHS4 =2.2′ -bis(2-mercaptophenylthio)diethylamine dianion, and L=NH3 , N2 H4 , PMe3 , CO, and NO+ . Since we know of no reliable experimental estimate of ΔEHL , we content ourselves with a comparison against the experimentally determined ground-state spin symmetry including, in so far as possible, finite-temperature effects. Together with the results of Papers I, II, and III, this paper provides a test of a large number of functionals against the high-spin/low-spin properties of a diverse set of Fe(II) compounds, making it possible to draw some particulary interesting conclusions. Trends among different classes of functionals are discussed and it is pointed out that there is at least one functional, namely, the OLYP generalized gradient approximation, which is able to give a reasonably good description of the delicate spin energetics of Fe(II) coordination compounds without resorting to hybrid functionals which require the relatively more expensive calculation of a Hartree–Fock-type exchange term. [ABSTRACT FROM AUTHOR]- Published
- 2005
- Full Text
- View/download PDF
9. Asymptotic neutron scattering laws for anomalously diffusing quantum particles.
- Author
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Kneller, Gerald R.
- Subjects
QUASIELASTIC neutron scattering ,PARTICLES (Nuclear physics) ,MEAN square algorithms ,FOURIER transforms ,MOMENTUM transfer - Abstract
The paper deals with a model-free approach to the analysis of quasielastic neutron scattering intensities from anomalously diffusing quantum particles. All quantities are inferred from the asymptotic form of their time-dependent mean square displacements which grow ?t
a , with 0 = a < 2. Confined diffusion (a = 0) is here explicitly included. We discuss in particular the intermediate scattering function for long times and the Fourier spectrum of the velocity autocorrelation function for small frequencies. Quantum effects enter in both cases through the general symmetry properties of quantum time correlation functions. It is shown that the fractional diffusion constant can be expressed by a Green-Kubo type relation involving the real part of the velocity autocorrelation function. The theory is exact in the diffusive regime and at moderate momentum transfers. [ABSTRACT FROM AUTHOR]- Published
- 2016
- Full Text
- View/download PDF
10. New tools for the systematic analysis and visualization of electronic excitations. II. Applications.
- Author
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Plasser, Felix, Bäppler, Stefanie A., Wormit, Michael, and Dreuw, Andreas
- Subjects
ELECTRONIC excitation ,EXCITON theory ,CARBON compounds ,ORGANIC compounds ,ORGANIC chemistry ,PARTICLES (Nuclear physics) - Abstract
The excited states of a diverse set of molecules are examined using a collection of newly implemented analysis methods. These examples expose the particular power of three of these tools: (i) natural difference orbitals (the eigenvectors of the difference density matrix) for the description of orbital relaxation effects, (ii) analysis of the one-electron transition density matrix in terms of an electronhole picture to identify charge resonance and excitonic correlation effects, and (iii) state-averaged natural transition orbitals for a compact simultaneous representation of several states. Furthermore, the utility of a wide array of additional analysis methods is highlighted. Five molecules with diverse excited state characteristics are chosen for these tasks: pyridine as a prototypical small heteroaromatic molecule, a model system of six neon atoms to study charge resonance effects, hexatriene in its neutral and radical cation forms to exemplify the cases of double excitations and spin-polarization, respectively, and a model iridium complex as a representative metal organic compound. Using these examples a number of phenomena, which are at first sight unexpected, are highlighted and their physical significance is discussed. Moreover, the generality of the conclusions of this paper is verified by a comparison of single- and multireference ab initio methods. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
11. Axion electrodynamics in topological materials.
- Author
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Akihiko Sekine and Kentaro Nomura
- Subjects
AXIONS ,ELECTRODYNAMICS ,QUANTUM chromodynamics ,HYPOTHETICAL particles ,MAGNETOELECTRIC effect ,PARTICLES (Nuclear physics) - Abstract
One of the intriguing properties characteristic to three-dimensional topological materials is the topological magnetoelectric phenomena arising from a topological term called the θ term. Such magnetoelectric phenomena are often termed the axion electrodynamics since the θ term has exactly the same form as the action describing the coupling between a hypothetical elementary particle, axion, and a photon. The axion was proposed about 40 years ago to solve the so-called strong CP problem in quantum chromodynamics and is now considered a candidate for dark matter. In this Tutorial, we overview theoretical and experimental studies on the axion electrodynamics in three-dimensional topological materials. Starting from the topological magnetoelectric effect in three-dimensional time-reversal invariant topological insulators, we describe the basic properties of static and dynamical axion insulators whose realizations require magnetic orderings. We also discuss the electromagnetic responses of Weyl semimetals with a focus on the chiral anomaly. We extend the concept of the axion electrodynamics in condensed matter to topological superconductors, whose responses to external fields can be described by a gravitational topological term analogous to the θ term. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
12. Effective-mode representation of non-Markovian dynamics: A hierarchical approximation of the spectral density. II. Application to environment-induced nonadiabatic dynamics.
- Author
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Hughes, Keith H., Christ, Clara D., and Burghardt, Irene
- Subjects
MARKOV spectrum ,SPECTRAL energy distribution ,DENSITY functionals ,PARTICLES (Nuclear physics) ,QUANTUM theory - Abstract
The non-Markovian approach developed in the companion paper [Hughes et al., J. Chem. Phys. 131, 024109 (2009)], which employs a hierarchical series of approximate spectral densities, is extended to the treatment of nonadiabatic dynamics of coupled electronic states. We focus on a spin-boson-type Hamiltonian including a subset of system vibrational modes which are treated without any approximation, while a set of bath modes is transformed to a chain of effective modes and treated in a reduced-dimensional space. Only the first member of the chain is coupled to the electronic subsystem. The chain construction can be truncated at successive orders and is terminated by a Markovian closure acting on the end of the chain. From this Mori-type construction, a hierarchy of approximate spectral densities is obtained which approach the true bath spectral density with increasing accuracy. Applications are presented for the dynamics of a vibronic subsystem comprising a high-frequency mode and interacting with a low-frequency bath. The bath is shown to have a striking effect on the nonadiabatic dynamics, which can be rationalized in the effective-mode picture. A reduced two-dimensional subspace is constructed which accounts for the essential features of the nonadiabatic process induced by the effective environmental mode. Electronic coherence is found to be preserved on the shortest time scale determined by the effective mode, while decoherence sets in on a longer time scale. Numerical simulations are carried out using either an explicit wave function representation of the system and overall bath or else an explicit representation of the system and effective-mode part in conjunction with a Caldeira–Leggett master equation. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
13. Calculation of nonadiabatic couplings with restricted open-shell Kohn-Sham density-functional theory.
- Author
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Billeter, Salomon R. and Egli, Daniel
- Subjects
PARTICLES (Nuclear physics) ,DENSITY functionals ,FUNCTIONAL analysis ,PERTURBATION theory ,APPROXIMATION theory ,ELECTRON-electron interactions - Abstract
This paper generalizes the recently proposed approaches for calculating the derivative couplings between adiabatic states in density-functional theory (DFT) based on a Slater transition-state density to transitions such as singlet-singlet excitations, where a single-determinant ansatz is insufficient. The proposed approach is based on restricted open-shell Frank et al. [J. Chem. Phys. 108, 4060 (1998)] theory used to describe a spin-adapted Slater transition state. To treat the dependence of electron-electron interactions on the nuclear positions, variational linear-response density-functional perturbation theory is generalized to reference states with an orbital-dependent Kohn-Sham Hamiltonian and nontrivial occupation patterns. The methods proposed in this paper are not limited to the calculation of derivative coupling vectors, but can also be used for the calculation of other transition matrix elements. Moreover, they can be used to calculate the linear response of open-shell systems to arbitrary external perturbations in DFT. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
14. Topological coarse graining of polymer chains using wavelet-accelerated Monte Carlo. II. Self-avoiding chains.
- Author
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Ismail, Ahmed E., Stephanopoulos, George, and Rutledge, Gregory C.
- Subjects
MONTE Carlo method ,NUCLEAR reactions ,PARTICLES (Nuclear physics) ,SCATTERING (Physics) ,NUMERICAL analysis ,MATHEMATICAL analysis ,MATHEMATICAL models - Abstract
In the preceding paper [A. E. Ismail, G. C. Rutledge, and G. Stephanopoulos J. Chem. Phys. (in press)] we introduced wavelet-accelerated Monte Carlo (WAMC), a coarse-graining methodology based on the wavelet transform, as a method for sampling polymer chains. In the present paper, we extend our analysis to consider excluded-volume effects by studying self-avoiding chains. We provide evidence that the coarse-grained potentials developed using the WAMC method obey phenomenological scaling laws, and use simple physical arguments for freely jointed chains to motivate these laws. We show that coarse-grained self-avoiding random walks can reproduce results obtained from simulations of the original, more-detailed chains to a high degree of accuracy, in orders of magnitude less time. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
15. Non-Markovian stochastic Schrödinger equations in different temperature regimes: A study of the spin-boson model.
- Author
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de Vega, Inés, Alonso, Daniel, Gaspard, Pierre, and Strunz, Walter T.
- Subjects
STOCHASTIC analysis ,LOW temperatures ,PARTICLES (Nuclear physics) ,HEAT ,SAMPLING (Process) ,MATHEMATICAL analysis - Abstract
Stochastic Schrödinger equations are used to describe the dynamics of a quantum open system in contact with a large environment, as an alternative to the commonly used master equations. We present a study of the two main types of non-Markovian stochastic Schrödinger equations, linear and nonlinear ones. We compare them both analytically and numerically, the latter for the case of a spin-boson model. We show in this paper that two linear stochastic Schrödinger equations, derived from different perspectives by Diósi, Gisin, and Strunz [Phys. Rev. A 58, 1699 (1998)], and Gaspard and Nagaoka [J. Chem. Phys. 13, 5676 (1999)], respectively, are equivalent in the relevant order of perturbation theory. Nonlinear stochastic Schrödinger equations are in principle more efficient than linear ones, as they determine solutions with a higher weight in the ensemble average which recovers the reduced density matrix of the quantum open system. However, it will be shown in this paper that for the case of a spin-boson system and weak coupling, this improvement does only occur in the case of a bath at high temperature. For low temperatures, the sampling of realizations of the nonlinear equation is practically equivalent to the sampling of the linear ones. We study further this result by analyzing, for both temperature regimes, the driving noise of the linear equations in comparison to that of the nonlinear equations. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
16. Electron and nuclear dynamics of molecular clusters in ultraintense laser fields. IV. Coulomb explosion of molecular heteroclusters.
- Author
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Last, Isidore and Jortner, Joshua
- Subjects
COULOMB excitation ,NUCLEAR excitation ,MOLECULAR dynamics ,PARTICLES (Nuclear physics) ,NUCLEAR reactions ,SCATTERING (Physics) - Abstract
In this paper we present a theoretical and computational study of the temporal dynamics and energetics of Coulomb explosion of (CD
4 )n and (CH4 )n (n=55–4213) molecular heteroclusters in ultraintense (I=1016 –1019 W cm-2 ) laser fields, addressing the manifestation of electron dynamics, together with nuclear energetic and kinematic effects on the heterocluster Coulomb instability. The manifestations of the coupling between electron and nuclear dynamics were explored by molecular dynamics simulations for these heteroclusters coupled to Gaussian laser fields (pulse width τ=25 fs), elucidating outer ionization dynamics, nanoplasma screening effects (being significant for I≤1017 W cm-2 ), and the attainment of cluster vertical ionization (CVI) (at I=1017 W cm-2 for cluster radius R0 ≤31 Å). Nuclear kinematic effects on heterocluster Coulomb explosion are governed by the kinematic parameter η=qC mA /qA mC for (CA4 )n clusters (A=H,D), where qj and mj (j=A,C) are the ionic charges and masses. Nonuniform heterocluster Coulomb explosion (η>1) manifests an overrun effect of the light ions relative to the heavy ions, exhibiting the expansion of two spatially separated subclusters, with the light ions forming the outer subcluster at the outer edge of the spatial distribution. Important features of the energetics of heterocluster Coulomb explosion originate from energetic triggering effects of the driving of the light ions by the heavy ions (C4+ for I=1017 –1018 W cm-2 and C6+ for I=1019 W cm-2 ), as well as for kinematic effects. Based on the CVI assumption, scaling laws for the cluster size (radius R0 ) dependence of the energetics of uniform Coulomb explosion of heteroclusters (η=1) were derived, with the size dependence of the average (Ej,av ) and maximal (Ej,M ) ion energies being Ej,av =aR0 2 and Ej,M =(5a/3)R0 2 , as well as for the ion energy distributions P(Ej )∝Ej 1/2 ; Ej ≤Ej,M . These results for uniform Coulomb explosion serve as benchmark reference data for the assessment of the effects of nonuniform explosion, where the CVI scaling law for the energetics still holds, with deviations of the a coefficient, which increase with increasing η. Kinematic effects (for η>1) result in an isotope effect, predicting the enhancement (by 9%–11%) of EH,av for Coulomb explosion of (C4+ H4 + )η (η=3) relative to ED,av for Coulomb explosion of (C4+ D4 + )η (η=1.5), with the isotope effect being determined by the ratio of the kinematic parameters for the pair of Coulomb exploding clusters. Kinematic effects for nonuniform explosion also result in a narrow isotope dependent energy distribution (of width ΔE) of the light ions (with ΔE/EH,av ≃0.3 and ΔE/ED,av ≃0.4), with the distribution peaking at the high energy edge, in marked contrast with the uniform explosion case. Features of laser-heterocluster interactions were inferred from the analyses of the intensity dependent boundary radii (R0 )I and the corresponding average D+ ion energies (ED,av )I , which provide a measure for optimization of the cluster size at intensity I for the neutron yield from dd nuclear fusion driven by Coulomb explosion (NFDCE) of these heteroclusters. We infer on the advantage of deuterium containing heteronuclear clusters, e.g., (CD4 )n in comparison to homonuclear clusters, e.g., (D2 )n/2 , for dd NFDCE, where the highly charged heavy ions (e.g., C4+ or C6+ ) serve as energetic and kinematic triggers driving the D+ ions to a high (10–200 keV) energy domain. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]- Published
- 2004
- Full Text
- View/download PDF
17. Excitation energies with linear response density matrix functional theory along the dissociation coordinate of an electron-pair bond in N-electron systems.
- Author
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van Meer, R., Gritsenko, O. V., and Baerends, E. J.
- Subjects
PHYSICS research ,COLLISIONAL excitation ,NUCLEAR excitation ,DENSITY matrices ,PARTICLES (Nuclear physics) ,CONDUCTION electrons ,ELECTRON research ,NATURAL orbitals - Abstract
Time dependent density matrix functional theory in its adiabatic linear response formulation delivers exact excitation energies ?a and oscillator strengths fa for two-electron systems if extended to the so-called phase including natural orbital (PINO) theory. The Löwdin-Shull expression for the energy of two-electron systems in terms of the natural orbitals and their phases affords in this case an exact phase-including natural orbital functional (PILS), which is non-primitive (contains other than just J and K integrals). In this paper, the extension of the PILS functional to N-electron systems is investigated. With the example of an elementary primitive NO functional (BBC1) it is shown that current density matrix functional theory ground state functionals, which were designed to produce decent approximations to the total energy, fail to deliver a qualitatively correct structure of the (inverse) response function, due to essential deficiencies in the reconstruction of the two-body reduced density matrix (2RDM). We now deduce essential features of an N-electron functional from a wavefunction Ansatz: The extension of the two-electron Löwdin-Shull wavefunction to the N-electron case informs about the phase information. In this paper, applications of this extended Löwdin-Shull (ELS) functional are considered for the simplest case, ELS(1): one (dissociating) two-electron bond in the field of occupied (including core) orbitals. ELS(1) produces high quality ωα(R) curves along the bond dissociation coordinate R for the molecules LiH, Li
2 , and BH with the two outer valence electrons correlated. All of these results indicate that response properties are much more sensitive to deficiencies in the reconstruction of the 2RDM than the ground state energy, since derivatives of the functional with respect to both the NOs and the occupation numbers need to be accurate. [ABSTRACT FROM AUTHOR]- Published
- 2014
- Full Text
- View/download PDF
18. Surprisal of a quantum state: Dynamics, compact representation, and coherence effects.
- Author
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Komarova, K., Remacle, F., and Levine, R. D.
- Subjects
QUANTUM theory ,QUANTUM states ,MOLECULAR physics ,PARTICLES (Nuclear physics) ,DISTRIBUTION (Probability theory) - Abstract
Progress toward quantum technologies continues to provide essential new insights into the microscopic dynamics of systems in phase space. This highlights coherence effects whether these are due to ultrafast lasers whose energy width spans several states all the way to the output of quantum computing. Surprisal analysis has provided seminal insights into the probability distributions of quantum systems from elementary particle and also nuclear physics through molecular reaction dynamics to system biology. It is therefore necessary to extend surprisal analysis to the full quantum regime where it characterizes not only the probabilities of states but also their coherence. In principle, this can be done by the maximal entropy formalism, but in the full quantum regime, its application is far from trivial [S. Dagan and Y. Dothan, Phys. Rev. D 26, 248 (1982)] because an exponential function of non-commuting operators is not easily accommodated. Starting from an exact dynamical approach, we develop a description of the dynamics where the quantum mechanical surprisal, a linear combination of operators, plays a central role. We provide an explicit route to the Lagrange multipliers of the system and identify those operators that act as the dominant constraints. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
19. Neutron transfer versus collective excitations in sub-barrier fusion dynamics of 28Si + 90,96Zr reactions.
- Author
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Gautam, Manjeet Singh, Vijay, Chahal, Rishi Pal, Khatri, Hitender, and Duhan, Sukhvinder
- Subjects
SILICON isotopes ,NEUTRONS ,MULTISENSOR data fusion ,PARTICLES (Nuclear physics) ,NUCLEAR fusion - Abstract
This paper examined the fusion of
28 Si with90,96 Zr-target by opting the energy dependent Woods-Saxon potential (EDWSP) model and code CCFULL. The CCFULL analysis suggested that for28 Si +90 Zr system, the vibrational excitations of90 Zr-isotope have been found to be very important while for28 Si +96 Zr system, in addition to multiphoton vibrational states of target, the considerations of nucleon transfer are essentially needed for the adequate addressal of the observed fusion data. In contrast, predictions based on EDWSP model appropriately recovered the fusion data of28 Si +90,96 Zr systems at sub-barrier realm. The EDWSP based results do not include various channel coupling effects explicitly but being the energy dependent nature of Woods-Saxon potential (WSP), the calculational results intrinsically incorporate the nuclear effects of the fusing systems. This unambiguously clarified that the energy dependent nature of the EDWSP generates analogous barrier modulations as emerged from the CCFULL analysis. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
20. Electrodynamics in flat spacetime of six dimensions.
- Author
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Yaremko, Yurij
- Subjects
ELECTRODYNAMICS ,NONLINEAR oscillations ,ELECTROMAGNETIC fields ,SPACETIME ,PARTICLES (Nuclear physics) - Abstract
This paper considers the dynamics of a classical charge in flat spacetime of six dimensions. The mass-shell relation of a free charge allows nonlinear oscillations. Having analyzed the problem of eigenvalues and eigenvectors of the Faraday tensor, we established the algebraic structure of the electromagnetic field in 6D. The classification scheme based on three field invariants is thoroughly elaborated. Using the basic algebraic properties of the electromagnetic field tensor, we examine the motion of a charge in a constant electromagnetic field. Its world line is a combination of hyperbolic and circular orbits that lie in three mutually orthogonal sheets of two dimensions. Within the braneworld scenario, we project the theory on the de Sitter space of four dimensions. As it turns out, spins of elementary particles themselves are manifestations of extra dimensions. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
21. Fundamental physics with cold radioactive atoms.
- Author
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Sakemi, Y., Aoki, T., Calabrese, R., Haba, H., Harada, K., Hayamizu, T., Ichikawa, Y., Jungmann, K., Kastberg, A., Kotaka, Y., Matsuda, Y., Matsuo, Y., Nagahama, H., Nakamura, K., Otsuka, M., Ozawa, N., Tanaka, K. S., Uchiyama, A., Ueno, H., and Willmann, L.
- Subjects
PARTICLE physics ,ELECTRIC dipole moments ,PARTICLES (Nuclear physics) ,CONDUCTION electrons ,PHYSICS ,CP violation ,OPTICAL lattices - Abstract
The fundamental symmetries, charge conjugation (C), parity (P) and time reversal (T), play a significant role in the Standard Model (SM) of elementary particle physics. Of these, T symmetry and the combined CP symmetry are the least well understood, and they hold valuable clues for unraveling the secrets of nature. All subatomic particles are postulated to possess an intrinsic property known as a permanent electric dipole moment (EDM). The EDM of an atom is a combination of those of each constituent particle and also CP-violating interactions between the particles. Being many-particle systems, atoms and molecules are ideal candidates for probing a rich variety of both T- and CP-violating interactions. Paramagnetic atoms, which have a single valence electron in their outer shell, are sensitive to subtle signals associated with CP violations in the leptonic sector, i.e., the EDM of the electron. At present, we are developing a high-intensity laser-cooled Fr factory at RIKEN accelerator facility in an attempt to evaluate the EDM of Fr to an accuracy of 10-30 ecm. Laser cooling is important for achieving highly accurate EDM measurements, since it allows long interaction times using an optical lattice. The current status of the laser-cooled Fr EDM experiments is presented in this paper. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
22. Nanoscale monoclinic domains in epitaxial SrRuO3 thin films deposited by pulsed laser deposition.
- Author
-
Ghica, C., Negrea, R. F., Nistor, L. C., Chirila, C. F., and Pintilie, L.
- Subjects
PULSED laser deposition ,THIN films ,TRANSMISSION electron microscopy ,ELECTRODES ,DIFFRACTIVE scattering ,PARTICLES (Nuclear physics) - Abstract
In this paper, we analyze the structural distortions observed by transmission electron microscopy in thin epitaxial SrRuO
3 layers used as bottom electrodes in multiferroic coatings onto SrTiO3 substrates for future multiferroic devices. Regardless of the nature and architecture of the multilayer oxides deposited on the top of the SrRuO3 thin films, selected area electron diffraction patterns systematically revealed the presence of faint diffraction spots appearing in forbidden positions for the SrRuO3 orthorhombic structure. High-resolution transmission electron microscopy (HRTEM) combined with Geometric Phase Analysis (GPA) evidenced the origin of these forbidden diffraction spots in the presence of structurally disordered nanometric domains in the SrRuO3 bottom layers, resulting from a strain-driven phase transformation. The local high compressive strain (-4% / -5%) measured by GPA in the HRTEM images induces a local orthorhombic to monoclinic phase transition by a cooperative rotation of the RuO6 octahedra. A further confirmation of the origin of the forbidden diffraction spots comes from the simulated diffraction patterns obtained from a monoclinic disordered SrRuO3 structure. [ABSTRACT FROM AUTHOR]- Published
- 2014
- Full Text
- View/download PDF
23. Magnetizability and rotational g tensors for density fitted local second-order Møller-Plesset perturbation theory using gauge-including atomic orbitals.
- Author
-
Loibl, Stefan and Schütza, Martin
- Subjects
NUCLEAR magnetic resonance ,QUANTUM chemistry ,PARTICLES (Nuclear physics) ,MAGNETIC resonance ,ATOMIC orbitals ,MAGNETIC fields - Abstract
In this paper, we present theory and implementation of an efficient program for calculating magnetizabilities and rotational g tensors of closed-shell molecules at the level of local second-order Møller- Plesset perturbation theory (MP2) using London orbitals. Density fitting is employed to factorize the electron repulsion integrals with ordinary Gaussians as fitting functions. The presented program for the calculation of magnetizabilities and rotational g tensors is based on a previous implementation of NMR shielding tensors reported by S. Loibl and M. Schütz [J. Chem. Phys. 137, 084107 (2012)]. Extensive test calculations show (i) that the errors introduced by density fitting are negligible, and (ii) that the errors of the local approximation are still rather small, although larger than for nuclear magnetic resonance (NMR) shielding tensors. Electron correlation effects for magnetizabilities are tiny for most of the molecules considered here. MP2 appears to overestimate the correlation contribution of magnetizabilities such that it does not constitute an improvement over Hartree-Fock (when comparing to higher-order methods like CCSD(T)). For rotational g tensors the situation is different and MP2 provides a significant improvement in accuracy over Hartree-Fock. The computational performance of the new program was tested for two extended systems, the larger comprising about 2200 basis functions. It turns out that a magnetizability (or rotational g tensor) calculation takes about 1.5 times longer than a corresponding NMR shielding tensor calculation. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
24. Adsorption of probe molecules in pillared interlayered clays: Experiment and computer simulation.
- Author
-
Gallardo, A., Guil, J. M., Lomba, E., Almarza, N. G., Khatib, S. J., Cabrillo, C., Sanz, A., and Pires, J.
- Subjects
SIMULATION methods & models ,SEPARATION (Technology) ,SURFACE chemistry ,MONTE Carlo method ,SOLUTION (Chemistry) ,PARTICLES (Nuclear physics) ,COMPUTER simulation ,BINDING agents - Abstract
In this paper we investigate the adsorption of various probe molecules in order to characterize the porous structure of a series of pillared interlayered clays (PILC). To that aim, volumetric and microcalorimetric adsorption experiments were performed on various Zr PILC samples using nitrogen, toluene, and mesitylene as probe molecules. For one of the samples, neutron scattering experiments were also performed using toluene as adsorbate. Various structural models are proposed and tested by means of a comprehensive computer simulation study, using both geometric and percolation analysis in combination with Grand Canonical Monte Carlo simulations in order to model the volumetric and microcalorimetric isotherms. On the basis of this analysis, we propose a series of structural models that aim at accounting for the adsorption experimental behavior, and make possible a microscopic interpretation of the role played by the different interactions and steric effects in the adsorption processes in these rather complex disordered microporous systems. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
25. Computational comparison of conductivity and mobility models for silicon nanowire devices.
- Author
-
Frey, M., Esposito, A., and Schenk, A.
- Subjects
NANOWIRES ,NANOSTRUCTURED materials ,PARTICLES (Nuclear physics) ,SILICON ,ELECTRIC wire - Abstract
In this paper, a comparison of three different models for the conductivity and mobility is given for the case of silicon nanowire devices in the presence of electron-phonon scattering. The consistency of all three models in the case of homogeneous nanowires is demonstrated. The scattering limited conductivity and mobility is a well defined quantity in this case. For nonhomogeneous systems like triple-gate nanowires FETs, these scattering limited quantities are no longer well defined for very short gate lengths. The quality of the underlying assumptions and the physical interpretation of the differences in the resulting transport characteristics are discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
26. The spin-free analogue of Mukherjee's state-specific multireference coupled cluster theory.
- Author
-
Datta, Dipayan and Mukherjee, Debashis
- Subjects
CLUSTER theory (Nuclear physics) ,OPERATOR theory ,PARTICLES (Nuclear physics) ,MOLECULAR orbitals ,EQUATIONS ,STATISTICAL correlation ,DYNAMICS - Abstract
In this paper, we develop a rigorously spin-adapted version of Mukherjee's state-specific multireference coupled cluster theory (SS-MRCC, also known as Mk-MRCC) [U. S. Mahapatra, B. Datta, and D. Mukherjee, J. Chem. Phys. 110, 6171 (1999)] for reference spaces comprising open-shell configurations. The principal features of our approach are as follows: (1) The wave operator Ω is written as Ω = ∑μΩμ|[lowercase_phi_synonym]μ>cμ, where {[lowercase_phi_synonym]μ} is the set of configuration state functions spanning a complete active space. (2) In contrast to the Jeziorski-Monkhorst Ansatz in spin-orbital basis, we write Ωμ as a power series expansion of cluster operators Rμ defined in terms of spin-free unitary generators. (3) The operators Rμ are either closed-shell-like n hole-n particle excitations (denoted as Tμ) or they involve valence (active) destruction operators (denoted as Sμ); these latter type of operators can have active-active scatterings, which can also carry the same active orbital labels (such Sμ's are called to have spectator excitations). (4) To simulate multiple excitations involving powers of cluster operators, we allow the Sμ's carrying the same active orbital labels to contract among themselves. (5) We exclude Sμ's with direct spectator scatterings. (6) Most crucially, the factors associated with contracted composites are chosen as the inverse of the number of ways the Sμ's can be joined among one another leading to the same excitation. The factors introduced in (6) have been called the automorphic factors by us. One principal thrust of this paper is to show that the use of the automorphic factors imparts a remarkable simplicity to the final amplitude equations: the equations consist of terms that are at most quartic in cluster amplitudes, barring only a few. In close analogy to the Mk-MRCC theory, the inherent linear dependence of the cluster amplitudes leading to redundancy is resolved by invoking sufficiency conditions, which are exact spin-free analogues of the spin-orbital based Mk-MRCC theory. This leads to manifest size-extensivity and an intruder-free formulation. Our formalism provides a relaxed description of the nondynamical correlation in presence of dynamical correlation. Pilot numerical applications to doublet systems, e.g., potential energy surfaces for the first two excited 2A' states of asymmetric H2S+ ion and the ground 2Σ+state of BeH radical are presented to assess the viability of our formalism over an wide range of nuclear geometries and the manifest avoidance of intruder state problem. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
27. Determination of interaction potentials of colloidal monolayers from the inversion of pair correlation functions: A two-dimensional predictor-corrector method.
- Author
-
Law, A. D. and Buzza, D. M. A.
- Subjects
MONOMOLECULAR films ,MONTE Carlo method ,PARTICLES (Nuclear physics) ,NUCLEAR physics education ,NUCLEAR physics - Abstract
The structure and stability of colloidal monolayers depend crucially on the effective pair potential u(r) between colloidal particles. In this paper, we develop a two-dimensional (2D) predictor-corrector method for extracting u(r) from the pair correlation function g(r) of dense colloidal monolayers. The method is based on an extension of the three-dimensional scheme of Rajagopalan and Rao [Phys. Rev. E 55, 4423 (1997)] to 2D by replacing the unknown bridge function B(r) with the hard-disk bridge function B
d (r); the unknown hard-disk diameter d is then determined using an iterative scheme. We compare the accuracy of our predictor-corrector method to the conventional one-step inversion schemes of hypernetted chain closure (HNC) and Percus–Yevick (PY) closure. Specifically we benchmark all three schemes against g(r) data generated from Monte Carlo simulation for a range of 2D potentials: exponential decay, Stillinger–Hurd, Lennard-Jones, and Derjaguin–Landau–Verwey–Overbeek. We find that for all these potentials, the predictor-corrector method is at least as good as the most accurate one-step method for any given potential, and in most cases it is significantly better. In contrast the accuracy of the HNC and PY methods relative to each other depends on the potential studied. The proposed predictor-corrector scheme is therefore a robust and more accurate alternative to these conventional one-step inversion schemes. [ABSTRACT FROM AUTHOR]- Published
- 2009
- Full Text
- View/download PDF
28. Variational and robust density fitting of four-center two-electron integrals in local metrics.
- Author
-
Reine, Simen, Tellgren, Erik, Krapp, Andreas, Kjærgaard, Thomas, Helgaker, Trygve, Jansik, Branislav, Høst, Stinne, and Salek, Paweł
- Subjects
DENSITY ,PARTICLES (Nuclear physics) ,COLLISIONS (Nuclear physics) ,LATTICE gauge theories ,POLARIZATION (Nuclear physics) - Abstract
Density fitting is an important method for speeding up quantum-chemical calculations. Linear-scaling developments in Hartree–Fock and density-functional theories have highlighted the need for linear-scaling density-fitting schemes. In this paper, we present a robust variational density-fitting scheme that allows for solving the fitting equations in local metrics instead of the traditional Coulomb metric, as required for linear scaling. Results of fitting four-center two-electron integrals in the overlap and the attenuated Gaussian damped Coulomb metric are presented, and we conclude that density fitting can be performed in local metrics at little loss of chemical accuracy. We further propose to use this theory in linear-scaling density-fitting developments. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
29. A Monte Carlo algorithm to study polymer translocation through nanopores. II. Scaling laws.
- Author
-
Gauthier, Michel G. and Slater, Gary W.
- Subjects
MONTE Carlo method ,PARTICLES (Nuclear physics) ,POLYMERS ,SOLID solutions ,NUCLEAR reactions ,SURFACE chemistry - Abstract
In the first paper of this series, we developed a new one-dimensional Monte Carlo approach for the study of flexible chains that are translocating through a small channel. We also presented a numerical scheme that can be used to obtain exact values for both the escape times and the escape probabilities given an initial pore-polymer configuration. We now present and discuss the fundamental scaling behaviors predicted by this Monte Carlo method. Our most important result is the fact that, in the presence of an external bias E, we observe a change in the scaling law for the translocation time τ as function of the polymer length N: In the general expression τ∼N
β /E, the exponent changes from β=1 for moderately long chains to β=1+ν or β=2ν for very large values of N (for Rouse and Zimm dynamics, respectively). We also observe an increase in the effective diffusion coefficient due to the presence of entropic pulling on unbiased polymer chains. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
30. E × B electron drift instability in Hall thrusters: Particle-in-cell simulations vs. theory.
- Author
-
Boeuf, J. P. and Garrigues, L.
- Subjects
DRIFT instability ,PLASMA drift ,HALL effect thruster ,PARTICLES (Nuclear physics) ,IONIZATION (Atomic physics) ,MATHEMATICAL models - Abstract
The
×E Electron Drift Instability (B ×E EDI), also called Electron Cyclotron Drift Instability, has been observed in recent particle simulations of Hall thrusters and is a possible candidate to explain anomalous electron transport across the magnetic field in these devices. This instability is characterized by the development of an azimuthal wave with wavelength in the mm range and velocity on the order of the ion acoustic velocity, which enhances electron transport across the magnetic field. In this paper, we study the development and convection of theB ×E EDI in the acceleration and near plume regions of a Hall thruster using a simplified 2D axial-azimuthal Particle-In-Cell simulation. The simulation is collisionless and the ionization profile is not-self-consistent but rather is given as an input parameter of the model. The aim is to study the development and properties of the instability for different values of the ionization rate (i.e., of the total ion production rate or current) and to compare the results with the theory. An important result is that the wavelength of the simulated azimuthal wave scales as the electron Debye length and that its frequency is on the order of the ion plasma frequency. This is consistent with the theory predicting destruction of electron cyclotron resonance of theB ×E EDI in the non-linear regime resulting in the transition to an ion acoustic instability. The simulations also show that for plasma densities smaller than under nominal conditions of Hall thrusters the field fluctuations induced by theB ×E EDI are no longer sufficient to significantly enhance electron transport across the magnetic field, and transit time instabilities develop in the axial direction. The conditions and results of the simulations are described in detail in this paper and they can serve as benchmarks for comparisons between different simulation codes. Such benchmarks would be very useful to study the role of numerical noise (numerical noise can also be responsible to the destruction of electron cyclotron resonance) or the influence of the period of the azimuthal domain, as well as to reach a better and consensual understanding of the physics. [ABSTRACT FROM AUTHOR]B - Published
- 2018
- Full Text
- View/download PDF
31. Random sequential adsorption of anisotropic particles. II. Low coverage kinetics.
- Author
-
Ricci, S. M., Talbot, J., Tarjus, G., and Viot, P.
- Subjects
ADSORPTION ,ANISOTROPY ,PARTICLES (Nuclear physics) - Abstract
We study the kinetics of random sequential adsorption (RSA) of anisotropic bodies (rectangles, ellipses, spherocylinders or, more precisely, discorectangles, and needles) at low-to-intermediate coverages. In this regime, the adsorption probability can be expressed as a power series in the coverage. We calculate numerically the second- and third-order coefficients of the series and compare the results to simulation data. The results for the low-coverage kinetics are then combined with the asymptotic results of Paper I [J. Chem. Phys. 97, xxxx (1992)] to construct approximate equations for the adsorption probability over the entire coverage range. While the equations provide a reasonably good description of the RSA kinetics, they produce unsatisfactory estimates of the saturation coverages. The effect of particle shape on the adsorption kinetics and surface structure is discussed. Finally, the available surface function is compared with that corresponding to equilibrium configurations of the adsorbed particles. [ABSTRACT FROM AUTHOR]
- Published
- 1992
- Full Text
- View/download PDF
32. On the properties of a primitive semiclassical surface hopping propagator for nonadiabatic quantum dynamics.
- Author
-
Yinghua Wu and Herman, Michael F.
- Subjects
QUANTUM theory ,SCHRODINGER equation ,WAVE mechanics ,PARTICLES (Nuclear physics) ,QUANTUM trajectories - Abstract
A previously developed nonadiabatic semiclassical surface hopping propagator [M. F. Herman J. Chem. Phys. 103, 8081 (1995)] is further studied. The propagator has been shown to satisfy the time-dependent Schrödinger equation (TDSE) through order h, and the O(h
2 ) terms are treated as small errors, consistent with standard semiclassical analysis. Energy is conserved at each hopping point and the change in momentum accompanying each hop is parallel to the direction of the nonadiabatic coupling vector resulting in both transmission and reflection types of hops. Quantum mechanical analysis and numerical calculations presented in this paper show that the h2 terms involving the interstate coupling functions have significant effects on the quantum transition probabilities. Motivated by these data, the h2 terms are analyzed for the nonadiabatic semiclassical propagator. It is shown that the propagator can satisfy the TDSE for multidimensional systems by including another type of nonclassical trajectories that reflect on the same surfaces. This h2 analysis gives three conditions for these three types of trajectories so that their coefficients are uniquely determined. Besides the nonadiabatic semiclassical propagator, a numerically useful quantum propagator in the adiabatic representation is developed to describe nonadiabatic transitions. [ABSTRACT FROM AUTHOR]- Published
- 2007
- Full Text
- View/download PDF
33. Local effective potential theory: Nonuniqueness of potential and wave function.
- Author
-
Sahni, Viraht, Slamet, Marlina, and Xiao-Yin Pan
- Subjects
DENSITY functionals ,POTENTIAL theory (Physics) ,POTENTIAL energy surfaces ,ELECTRONIC systems ,MATHEMATICAL analysis ,PARTICLES (Nuclear physics) ,QUANTUM chemistry - Abstract
In local effective potential energy theories such as the Hohenberg-Kohn-Sham density functional theory (HKS-DFT) and quantal density functional theory (Q-DFT), electronic systems in their ground or excited states are mapped to model systems of noninteracting fermions with equivalent density. From these models, the equivalent total energy and ionization potential are also obtained. This paper concerns (i) the nonuniqueness of the local effective potential energy function of the model system in the mapping from a nondegenerate ground state, (ii) the nonuniqueness of the local effective potential energy function in the mapping from a nondegenerate excited state, and (iii) in the mapping to a model system in an excited state, the nonuniqueness of the model system wave function. According to nondegenerate ground state HKS-DFT, there exists only one local effective potential energy function, obtained as the functional derivative of the unique ground state energy functional, that can generate the ground state density. Since the theorems of ground state HKS-DFT cannot be generalized to nondegenerate excited states, there could exist different local potential energy functions that generate the excited state density. The constrained-search version of HKS-DFT selects one of these functions as the functional derivative of a bidensity energy functional. In this paper, the authors show via Q-DFT that there exist an infinite number of local potential energy functions that can generate both the nondegenerate ground and excited state densities of an interacting system. This is accomplished by constructing model systems in configurations different from those of the interacting system. Further, they prove that the difference between the various potential energy functions lies solely in their correlation-kinetic contributions. The component of these functions due to the Pauli exclusion principle and Coulomb repulsion remains the same. The existence of the different potential energy functions as viewed from the perspective of Q-DFT reaffirms that there can be no equivalent to the ground state HKS-DFT theorems for excited states. Additionally, the lack of such theorems for excited states is attributable to correlation-kinetic effects. Finally, they show that in the mapping to a model system in an excited state, there is a nonuniqueness of the model system wave function. Different wave functions lead to the same density, each thereby satisfying the sole requirement of reproducing the interacting system density. Examples of the nonuniqueness of the potential energy functions for the mapping from both ground and excited states and the nonuniqueness of the wave function are provided for the exactly solvable Hooke’s atom. The work of others is also discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
34. Control of structure and photophysical properties by protonation and subsequent intramolecular hydrogen bonding.
- Author
-
Mengtao Sun
- Subjects
HYDROGEN bonding ,LUMINESCENCE ,PARTICLES (Nuclear physics) ,QUANTUM theory ,DIPOLE moments ,PHYSICS - Abstract
Protonation and subsequent intramolecular hydrogen bonding as methods to control chain structure and tune luminescence in heteroatomic conjugated polymers were reported experimentally [A. P. Monkman et al., J. Am. Chem. Soc. 124, 6049 (2002)]. In this paper, the structure and photophysical properties of the model teraryl compound of phenylene-pyridylene copolymer before and after protonation are theoretically studied with quantum chemistry methods. From the optimized ground states, intramolecular hydrogen bonding to the adjacent oxygen atom in the alkoxy substituent planarizes the backbone of the molecules, and the optimized detailed results of compound 9 before and after protonation, such as the dihedral angles between the central benzene and the two pyridyl rings, the bond lengths, and the bond angles, are consistent with the experimental results. From the results of the calculated excited states, the protonation and subsequent intramolecular hydrogen bonding result in the redshifts of the absorption, the increase of the ionization energy, the increase of the electron affinity, the decrease of the energy difference of the highest occupied molecular orbital and lowest unoccupied molecular orbital, the decrease of the binding gap, and the delocalization of the electron-hole coherence. The photophysical properties of compound 9 before and after protonation are further studied with a three-dimensional real-space analysis method of transition and charge difference densities (study transition dipole moment and charge transfer in the absorption and fluorescence processes) and two-dimensional real-space analysis method of transition density matrices (study the electron-hole coherence and the excitation delocalization). The calculated results show theoretically an insight understanding on the influence of the protonation and subsequent intramolecular hydrogen bonding to chain structure and photophysical properties. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
35. Damped and thermal motion of laser-aligned hydrated macromolecule beams for diffraction.
- Author
-
Starodub, D., Doak, R. B., Schmidt, K., Weierstall, U., Wu, J. S., Spence, J. C. H., Howells, M., Marcus, M., Shapiro, D., Barty, A., and Chapman, H. N.
- Subjects
PROTEINS ,VIBRATION (Mechanics) ,WAVES (Physics) ,OPTICAL diffraction ,PARTICLES (Nuclear physics) ,VISCOELASTICITY ,MOLECULES - Abstract
We consider a monodispersed Rayleigh droplet beam of water droplets doped with proteins. An intense infrared laser is used to align these droplets. The arrangement has been proposed for electron- and x-ray-diffraction studies of proteins which are difficult to crystallize. This paper considers the effect of thermal fluctuations on the angular spread of alignment in thermal equilibrium, and relaxation phenomena, particularly the damping of oscillations excited as the molecules enter the field. The possibility of adiabatic alignment is also considered. We find that damping times in a high-pressure gas cell as used in x-ray-diffraction experiments are short compared with the time taken for molecules to traverse the beam and that a suitably shaped field might be used for electron-diffraction experiments in vacuum to provide adiabatic alignment, thus obviating the need for a damping gas cell. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
36. Appraisal of the performance of nonhybrid density functional methods in characterization of the Al4C molecule.
- Author
-
Zubarev, Dmitry Yu. and Boldyrev, Alexander I.
- Subjects
DENSITY functionals ,FUNCTIONAL analysis ,QUANTUM chemistry ,POTENTIAL energy surfaces ,PARTICLES (Nuclear physics) ,ATOMIC orbitals - Abstract
In three recent publications it was predicted that an Al
4 C molecule is planar on the basis of nonhybrid density functional calculations. These conclusions contradict our earlier predictions that Al4 C is tetrahedral. In order to resolve the controversy we probed in this paper a potential energy surface of Al4 C using a large variety of theoretical methods including multiconfigurational methods and a variety of one-electron basis sets. We confirmed that the nonhybrid Becke’s exchange with Perdew–Wang 1991 correlation functional density functional method predicts that Al4 C has a planar structure in agreement with the reports of the other three groups. However, in this paper we have shown that high level ab initio calculations at the coupled cluster with singles, doubles, and noniterative triples and at the complete active space self-consistent field followed by multireference configurational interaction levels of theory confirm our earlier prediction that Al4 C is indeed tetrahedral. The failure of nonhybrid density functional methods to correctly characterize the global minimum structure of Al4 C demonstrates that it is dangerous to rely solely on these density functional methods in characterization of new molecules and clusters, where experimental structure is not known. [ABSTRACT FROM AUTHOR]- Published
- 2005
- Full Text
- View/download PDF
37. Four-body Faddeev-type calculation of the K¯NNN system.
- Author
-
Shevchenko, N. V., Meyer, Curtis, and Schumacher, Reinhard A.
- Subjects
QUASI bound states ,PARTICLES (Nuclear physics) - Abstract
The paper is devoted to four-body Faddeev-type AGS equations, written down for the K ¯ NNN system, which is a system consisting of an antikaon and three nucleons. The aim is to find possible quasi-bound state in the system and calculate its properties. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
38. Drell-Yan program at SeaQuest.
- Author
-
Tadepalli, Arun S., Gilman, Ronald A., Meyer, Curtis, and Schumacher, Reinhard A.
- Subjects
PARTICLES (Nuclear physics) ,PROTON beams ,PLASMA beam injection heating ,ORDER picking systems ,PHYSICS ,INJECTORS ,PHOTONS - Abstract
Fermilab E906/SeaQuest is an experiment aimed at studying the anti-quark distributions of nucleons and nuclei. The experiment uses a 120 GeV/c proton beam extracted from the Main Injector at Fermilab to collide with various solid and cryogenic targets to study a variety of physics topics ranging from light anti-quark flavor asymmetry in the nucleon sea to dark photons. The experiment takes advantage of the Drell-Yan process in order to probe specifically the high-x anti-quark distributions of the target nucleus. The acceptance of the spectrometer is tuned to explore the unprecedentedly high Bjorken-x region, thereby extending our knowledge of the anti-quark sea structure of nucleons and nuclei. Some of the physics goals from the Drell-Yan program at SeaQuest and the current status of some analyses are reported in this paper. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
39. Progress in Kaon Photoproduction off the Nucleon in Six Isospin Channels.
- Author
-
Mart, T.
- Subjects
ISOBARIC spin ,PARTICLE detectors ,PARTICLES (Nuclear physics) ,WAVE analysis ,PROGRESS - Abstract
Motivated by the recent abundant experimental data obtained from the continuous and heavy duty accelerators along with the precise and modern particle detectors, we have intensively analyzed the elementary kaon photoproduction processes from their production thresholds up to W ≈ 3 GeV in the last two decades. All possible isospin channels are considered in the analysis because recently experimental data have been available in all channels. This includes γp → K
+ Λ, K+ Σ0 , K0 Σ+ processes off the proton and γn → K0 Λ, K+ Σ− , K0 Σ0 processes off the neuron. In this proceedings paper we briefly report on the latest progress of our analysis. There are two approaches that have been used for this purpose, i.e., the isobar model which is based on the Effective Lagrangian Theory and the partial wave analysis, in which the corresponding multipoles are parameterized by means of the Breit-Wigner form. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
40. Angle effect in laser nanopatterning with particle-mask.
- Author
-
Wang, Z.B., Hong, M.H., Luk'yanchuk, B.S., Lin, Y., Wang, Q.F., and Chong, T.C.
- Subjects
NANOSTRUCTURES ,LASERS ,MAGNETIC fields ,LASER beams ,LIGHT scattering ,OPTICAL reflection ,PARTICLES (Nuclear physics) - Abstract
Parallel nanostructuring of substrate surface with particle-mask is a promising technology that may significantly improve the patterning speed under single laser pulse irradiation. In this paper, the influence of the incidence wave angle on the pattern structures is investigated. Polystyrene spherical particles were deposited on the surface in a monolayer form by self-assembly. The sample was then irradiated with 248 nm KrF laser at different incidence angles α. It is found that nanostructures can be formed at different positions with different incidence angles. Both round-shape and comet-shape nanostructures can be produced. By varying the incidence angles, the depth of the nanostructures can also be controlled. To explain the different nanostructures produced at different angles, the intensity field distributions under the particle were calculated according to an exact model for light scattering by a sphere on the substrate (P. A. Bobbert and J. Vlieger, Physica A 137A, 209 1986). The main equation in the original model was reformed for the ease of numerical simulation. A method was proposed to calculate the total electric and magnetic field as an extension to the model. The theoretical results are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
41. Time evolution of plasma afterglow produced by femtosecond laser pulses.
- Author
-
Martirosyan, A.E., Altucci, C., Bruno, A., de Lisio, C., Porzio, A., and Solimeno, S.
- Subjects
PLASMA gases ,FEMTOCHEMISTRY ,LASER beams ,PARTICLES (Nuclear physics) ,COLLISIONS (Nuclear physics) ,ELECTRON-molecule collisions ,ULTRASHORT laser pulses ,PICOSECOND pulses - Abstract
In this paper we investigate the time evolution of laser plasmas generated in atmospheric air by ultrashort (100 fs) laser pulses. The detected quantity is the time integrated photon yield emitted by the plasma, which monotonically depends on the amount of energy transferred by the laser pulses to the plasma. We study the effect of a preionizing pulse on the efficiency of plasma generation by a second “probe” pulse and demonstrate that preionization results into a considerable increase of the overall photon yield emitted by the plasma. An explanation of this phenomenon relies on the fact that the larger the electron density experienced by the probe pulse, the more effective the energy transfer from the probe pulse to the residual plasma, the more intense is the light from the plasma. With this concept in mind and by relying on a pump-probe technique, we also measure the total photon yield emitted by the plasma produced by the combination of the two pulses, as a function of their relative delay time. We observe a considerable increase in the plasma brightness for delay times much longer than the laser pulse duration. This phenomenon is associated with an increase of the electron density even after the end of the pump pulse, due to secondary electron-impact ionization originating from highly-energetic primary photoelectrons, and to superelastic electron-molecule collisions. We also develop a simplified model describing the time evolution of the electron and ion densities and the electron temperature. From the calculated time evolution of these quantities produced by a single laser pulse, we can predict with a good approximation the main features of the plasma generated by an ultrashort laser pulse. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
42. Electron and nuclear dynamics of molecular clusters in ultraintense laser fields. III. Coulomb explosion of deuterium clusters.
- Author
-
Last, Isidore and Jortner, Joshua
- Subjects
MOLECULAR dynamics ,CLUSTER analysis (Statistics) ,PARTICLES (Nuclear physics) ,MICROCLUSTERS ,GAUSSIAN distribution ,GAUSSIAN processes ,IONIZATION (Atomic physics) - Abstract
In this paper we present a theoretical and computational study of the energetics and temporal dynamics of Coulomb explosion of molecular clusters of deuterium (D
2 )n/2 (n=480-7.6×104 , cluster radius R0 =13.1–70 Å) in ultraintense laser fields (laser peak intensity I=1015 –1020 W cm-2 ). The energetics of Coulomb explosion was inferred from the dependence of the maximal energy EM and the average energy Eav of the product D+ ions on the laser intensity, the laser pulse shape, the cluster radius, and the laser frequency. Electron dynamics of outer cluster ionization and nuclear dynamics of Coulomb explosion were investigated by molecular dynamics simulations. Several distinct laser pulse shape envelopes, involving a rectangular field, a Gaussian field, and a truncated Gaussian field, were employed to determine the validity range of the cluster vertical ionization (CVI) approximation. The CVI predicts that Eav , EM ∝R0 2 and that the energy distribution is P(E)∝E1/2 . For a rectangular laser pulse the CVI conditions are satisfied when complete outer ionization is obtained, with the outer ionization time toi being shorter than both the pulse width and the cluster radius doubling time τ2 . By increasing toi , due to the increase of R0 or the decrease of I, we have shown that the deviation of Eav from the corresponding CVI value (Eav CVI ) is (Eav CVI -Eav )/Eav CVI ≃(toi /2.91τ2 )2 . The Gaussian pulses trigger outer ionization induced by adiabatic following of the laser field and of the cluster size, providing a pseudo-CVI behavior at sufficiently large laser fields. The energetics manifest the existence of a finite range of CVI size dependence, with the validity range for the applicability of the CVI being R0 ≤(R0 )I , with (R0 )I representing an intensity dependent boundary radius. Relating electron dynamics of outer ionization to nuclear dynamics for Coulomb explosion induced by a Gaussian pulse, the boundary radius (R0 )I and the corresponding ion average energy (Eav )I were inferred from simulations and described in terms of an electrostatic model. Two independent estimates of (R0 )I , which involve the cluster size where the CVI relation breaks down and the cluster size for the attainment of complete outer ionization, are in good agreement with each other, as well as with the electrostatic model for cluster barrier suppression. The relation (Eav )I ∝(R0 )I 2 provides the validity range of the pseudo-CVI domain for the cluster sizes and laser intensities, where the energetics of D+ ions produced by Coulomb explosion of (D)n clusters is optimized. The currently available experimental data [Madison et al., Phys. Plasmas 11, 1 (2004)] for the energetics of Coulomb explosion of (D)n clusters (Eav =5–7 keV at I=2×1018 W cm-2 ), together with our simulation data, lead to the estimates of R0 =51–60 Å, which exceed the experimental estimate of R0 =45 Å. The predicted anisotropy of the D+ ion energies in the Coulomb explosion at I=1018 W cm-2 is in accord with experiment. We also explored the laser frequency dependence of the energetics of Coulomb explosion in the range ν=0.1–2.1 fs-1 (λ=3000–140 nm), which can be rationalized in terms of the electrostatic model. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]- Published
- 2004
- Full Text
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43. A semiclassical generalized quantum master equation for an arbitrary system-bath coupling.
- Author
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Shi, Qiang and Geva, Eitan
- Subjects
QUANTUM theory ,EQUATIONS ,COUPLING constants ,PARTICLES (Nuclear physics) ,KERNEL functions ,FUNCTIONAL analysis - Abstract
The NakajimaZwanzig generalized quantum master equation (GQME) provides a general, and formally exact, prescription for simulating the reduced dynamics of a quantum system coupled to a, possibly anharmonic, quantum bath. In this equation, a memory kernel superoperator accounts for the influence of the bath on the dynamics of the system. In a previous paper [Q. Shi and E. Geva, J. Chem. Phys. 119, 12045 (2003)] we proposed a new approach to calculating the memory kernel, in the case of arbitrary system-bath coupling. Within this approach, the memory kernel is obtained by solving a set of two integral equations, which requires a new type of two-time system-dependent bath correlation functions as input. In the present paper, we consider the application of the linearized semiclassical (LSC) approximation for calculating those correlation functions, and subsequently the memory kernel. The new approach is tested on a benchmark spin-boson model. Application of the LSC approximation for calculating the relatively short-lived memory kernel, followed by a numerically exact solution of the GQME, is found to provide an accurate description of the relaxation dynamics. The success of the proposed LSCGQME methodology is contrasted with the failure of both the direct application of the LSC approximation and the weak coupling treatment to provide an accurate description of the dynamics, for the same model, except at very short times. The feasibility of the new methodology to anharmonic systems is also demonstrated in the case of a two level system coupled to a chain of LennardJones atoms. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
44. Making the Quantum Scattering of Fundamental Particles Accessible.
- Author
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Day, James, Liao, Theresa Yu-Huan, Hoyt, Char, and Can, Oguzhan
- Subjects
PARTICLES (Nuclear physics) ,QUANTUM scattering ,SCATTERING (Physics) ,PICTURES ,PHYSICS ,FEYNMAN diagrams - Abstract
This paper shares a hands-on activity that introduces Feynman diagrams and the accompanying idea of using pictorial representations to describe the behavior of subatomic particles—specifically, for electrons and photons—in place of mathematical expressions. Built collaboratively by scientists and artists, it exemplifies a triumph of lateral thinking by highlighting the vital role Feynman diagrams have played in modern physics. While the student may initially treat this activity as a glimpse into the quantum realm, the teacher should recognize this as a demonstration of lateral thinking as an insight tool. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
45. A deformation parameters estimation and intrinsic electric quadrupole moment of 58-60Ni isotopes.
- Author
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Attosh, Hadeel Abd Alelah and Obeed, Fatema Hameed
- Subjects
QUADRUPOLE moments ,PARAMETER estimation ,ISOTOPES ,NEUTRONS ,PARTICLES (Nuclear physics) ,ENERGY levels (Quantum mechanics) - Abstract
This study demonstrates some nuclear properties that have been calculated of 58-60Ni nuclei such as positive energy levels ,electric quadrupole transitions, intrinsic quadrupole moment and factors of deformation. Nushell@MSU code was utilized for f5p model space with Van Hienen - Chung -Wildenthal (f5pvh) interaction. The calculations are carried out by utilizing three sets of effective charges obtained from Bohr - Mottelson model also default and appropriate effective charges for valance nucleons(protons and neutrons). A comparison has been made between theoretic effects with the available experimental data. The comparison shows that the energy levels , transition probabilities, intrinsic quadrupole moment and quadrupole deformation parameter are agreed well especially at effective charges of Bohr - Mottelson model and appropriate effective charges. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
46. Field emission from multiwall carbon nanotubes on paper substrates.
- Author
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Lyth, S. M. and Silva, S. R. P.
- Subjects
FIELD emission ,SURFACE roughness ,CARBON nanotubes ,ELECTRODES ,NANOTUBES ,PARTICLES (Nuclear physics) - Abstract
The authors report extremely low electron field emission thresholds from acid oxidized multiwall carbon nanotubes deposited on paper substrates by dip coating in an aqueous nanotube ink. Using paper substrates of differing surface roughness, field emission threshold fields ranging from 0.8 to 11.6 V/μm were observed, varying in an approximate inverse linear log relationship with the surface roughness of the underlying paper substrate. This study shows how field emission from supported nanotube films can be tailored via the morphology of the scaffold substrate, and how these composite electrodes can be straightforwardly fabricated on cheap, flexible substrates. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
47. Nanostructure evolution in joining of Al and Fe nanoparticles with femtosecond laser irradiation.
- Author
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Z. Jiao, H. Huang, L. Liu, A. Hu, Duley, W., He, P., and Y. Zhou
- Subjects
NANOSTRUCTURED materials ,NANOPARTICLES ,ELECTRON microscopy ,FEMTOSECOND lasers ,PARTICLES (Nuclear physics) - Abstract
The joining of Al-Fe nanoparticles (NPs) by femtosecond (fs) laser irradiation is reported in this paper. Fe and Al NPs were deposited on a carbon film in vacuum via fs laser ablation. Particles were then exposed to multiple fs laser pulses at fluences between 0.5 and 1.3 mJ/cm
2 . Transmission Electron Microscopy (TEM) and Electron Diffraction X-ray observations indicate that Al and Fe NPs bond to each other under these conditions. For comparison, bonding of Al to Al and Fe to Fe NPs was also investigated. The nanostructure, as observed using TEM, showed that individual Al NPs were monocrystalline while individual Fe NPs were polycrystalline prior to joining and that these structures are retained after the formation of Al-Al and Fe-Fe NPs. Al-Fe NPs produced by fs laser joining exhibited a mixed amorphous and crystalline phase at the interface. Bonding is suggested to originate from intermixing within a region of high field intensity between particles. [ABSTRACT FROM AUTHOR]- Published
- 2014
- Full Text
- View/download PDF
48. Particle-particle and quasiparticle random phase approximations: Connections to coupled cluster theory.
- Author
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Scuseria, Gustavo E., Henderson, Thomas M., and Bulik, Ireneusz W.
- Subjects
PHYSICS research ,CLUSTER theory (Nuclear physics) ,QUASIPARTICLES ,CALCULATIONS & mathematical techniques in atomic physics ,PARTICLE physics ,PARTICLES (Nuclear physics) ,EXCITON theory ,WAVE functions - Abstract
We establish a formal connection between the particle-particle (pp) random phase approximation (RPA) and the ladder channel of the coupled cluster doubles (CCD) equations. The relationship between RPA and CCD is best understood within a Bogoliubov quasiparticle (qp) RPA formalism. This work is a follow-up to our previous formal proof on the connection between particle-hole (ph) RPA and ring-CCD. Whereas RPA is a quasibosonic approximation, CC theory is a 'correct bosonization' in the sense that the wavefunction and Hilbert space are exactly fermionic, yet the amplitude equations can be interpreted as adding different quasibosonic RPA channels together. Coupled cluster theory achieves this goal by interacting the ph (ring) and pp (ladder) diagrams via a third channel that we here call 'crossed-ring' whose presence allows for full fermionic antisymmetry. Additionally, coupled cluster incorporates what we call 'mosaic' terms which can be absorbed into defining a new effective one-body Hamiltonian. The inclusion of these mosaic terms seems to be quite important. The pp-RPA and qp-RPA equations are textbook material in nuclear structure physics but are largely unknown in quantum chemistry, where particle number fluctuations and Bogoliubov determinants are rarely used. We believe that the ideas and connections discussed in this paper may help design improved ways of incorporating RPA correlation into density functionals based on a CC perspective. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
49. Coupled multiphysics, barrier localization, and critical radius effects in embedded nanowire superlattices.
- Author
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Prabhakar, Sanjay, Melnik, Roderick, and Bonilla, Luis L
- Subjects
NANOWIRES ,SUPERLATTICES ,ELECTROMAGNETIC fields ,WURTZITE ,PARTICLES (Nuclear physics) ,CATHODE rays - Abstract
The new contribution of this paper is to develop a cylindrical representation of an already known multiphysics model for embedded nanowire superlattices (NWSLs) of wurtzite structure that includes a coupled, strain dependent 8-band k·p Hamiltonian in cylindrical coordinates and investigate the influence of coupled piezo-electromechanical effects on the barrier localization and critical radius in such NWSLs. The coupled piezo-electromechanical model for semiconductor materials takes into account the strain, piezoelectric effects, and spontaneous polarization. Based on the developed 3D model, the band structures of electrons (holes) obtained from results of modeling in Cartesian coordinates are in good agreement with those values obtained from our earlier developed 2D model in cylindrical coordinates. Several parameters such as lattice mismatch, piezo-electric fields, valence, and conduction band offsets at the heterojunction of AlxGa1-xN/GaN superlattice can be varied as a function of the Al mole fraction. When the band offsets at the heterojunction of AlxGa1-xN/GaN are very small and the influence of the piezo-electromechanical effects can be minimized, then the barrier material can no longer be treated as an infinite potential well. In this situation, it is possible to visualize the penetration of the Bloch wave function into the barrier material that provides an estimation of critical radii of NWSLs. In this case, the NWSLs can act as inversion layers. Finally, we investigate the influence of symmetry of the square and cylindrical NWSLs on the band structures of electrons in the conduction band. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
50. Analyzing Railguns with Excel: Simple Numerical Integration for the Classroom.
- Author
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Font, Gabriel I. and Dills, Anthony N.
- Subjects
PARTICLES (Nuclear physics) ,RAILGUNS ,LORENTZ force ,ELECTROMAGNETIC theory ,ELECTRIC inductance - Abstract
Any teacher of elementary physics can attest to the waning interest of students when all they are exposed to are boxes sliding down planes. In an effort to motivate interest, it is often useful to borrow examples from the real world. This way the students find it easy to identify the relevance of the subject matter. In addition, high-tech applications can be inspirational and serve to motivate the students to look deeper into the phenomena. One example of a technology that makes students sit up and pay attention are railguns. They are easily demonstrated using YouTube videos, especially now that the U.S. Navy has begun to release publicity videos of their latest designs and associated fact sheet and papers. This paper gives some background and simple models of the relevant physics of railguns. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
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