302 results
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2. High-precision Ramsey-comb spectroscopy on molecular deuterium for tests of molecular quantum theory.
- Author
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Roth, Charlaine, de Velasco, Andrés Martínez, Gründeman, Elmer L., Collombon, Mathieu, Beyer, Maximilian, Barbé, Vincent, and Eikema, Kjeld S. E.
- Subjects
MOLECULAR spectroscopy ,QUANTUM theory ,MOLECULAR theory ,PHYSICAL laws ,MOLECULAR beams ,COLLISION induced dissociation ,OPTICAL frequency conversion - Abstract
Precision spectroscopy of simple, calculable molecules has become an important tool to compare experiments with theory in an effort to test our understanding of the fundamental laws of physics. For this purpose, we have measured the E F 1 Σ g + (v ′ = 0 , N ′ = 0) ← X 1 Σ g + (v ″ = 0 , N ″ = 0) transition frequency of molecular deuterium ( D 2 ) with unprecedented accuracy. We use Ramsey-Comb spectroscopy at deep-ultraviolet wavelengths (201 nm) with a two-photon, Doppler-free interrogation scheme. The resulting transition frequency is f = 2 , 981 , 779 , 227 , 578 (19) kHz. The 1-σ uncertainty of 19 kHz represents an improvement of more than two orders of magnitude compared to the best previous measurement. In this paper, we give an extensive description of our methods and the experimental apparatus that we employed. Particular attention is given to aspects that we recently improved, such as the frequency comb laser system, the method of signal recording, and the cryogenic D 2 molecular beam apparatus. In combination with future measurements of the ionisation energy of the EF state, our measurement paves the way for an improved determination of the ground state ionisation and dissociation energy of molecular deuterium. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
3. Efficient matrix factorisation of the modular path integral for extended systems.
- Author
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Kundu, Sohang and Makri, Nancy
- Subjects
PATH integrals ,DENSITY matrices ,EXCITON theory ,FACTORIZATION ,QUANTUM theory ,FAST Fourier transforms - Abstract
The modular path integral (MPI) formulation offers a numerically exact, versatile, and highly efficient approach to the quantum dynamics of extended systems characterised by a single-file arrangement of units with short-range interactions, such as hydrocarbons, molecular aggregates with exciton couplings, or spin chains. Rather than propagating the many-particle wavefunction or density matrix in time in the usual stepwise fashion, the MPI scheme proceeds by sequentially integrating over each unit after linking its quantum paths to those of its neighbour and leads to linear scaling with system length. This paper shows that the linking matrix can be further decomposed into a diagonal matrix and a product of low-dimensional matrices, which can be applied sequentially. This factorisation changes the cost scaling from L
2 to L log L , where L is the number of quantum paths, leading to dramatic savings that are analogous to those attained by the fast Fourier transform algorithm and allowing application of the MPI procedure to systems with larger units and to longer propagation times. Applications to spin chains and to electron-vibration dynamics in a large molecular aggregate illustrate the efficiency of the algorithm. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
4. Persistence of non-local correlations and quantum information theoretic measures in the thermal state of frustrated molecular wheels.
- Author
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Tribedi, Amit
- Subjects
QUANTUM chemistry ,QUANTUM entanglement ,QUANTUM theory ,SINGLE molecule magnets ,MOLECULAR structure ,CHEMICAL synthesis - Abstract
Genuine quantumness present in quantum systems is the resource for implementing quantum information and computation protocols which can outperform the classical counterparts. These quantumness measures encompass non-local ones known as quantum entanglement (QE) and quantum information theoretic ones, e.g. quantum discord (QD). In this paper, some well-known measures of QE and QD have been studied in two wheel-like frustrated molecular magnetic systems, with special emphasis on the survival of the measures in the thermal states. A molecular magnetic system similar to the first one (with half-integer spins) has already been synthesised using coordination chemistry, and the other is hypothetical, where the dominant interaction is the spin–spin exchange interaction. Exact numerical diagonalisation methods have been used. Some non-trivial features, like nonmonotonicity of threshold temperatures with external magnetic field, persistence of multipartite entanglement and QD over bipartite entanglement, have been found. The measures, being operational ones, can be used to realise the resource of quantumness in experiments. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
5. A friendly review of absorbing boundary conditions and perfectly matched layers for classical and relativistic quantum waves equations.
- Author
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Antoine, X., Lorin, E., and Tang, Q.
- Subjects
BOUNDARY value problems ,WAVE equation ,QUANTUM theory ,NUMERICAL analysis ,DIRAC equation - Abstract
The aim of this paper is to describe concisely the recent theoretical and numerical developments concerningabsorbing boundary conditions and perfectly matched layers for solving classical and relativistic quantum waves problems. The equations considered in this paper are the Schrödinger, Klein–Gordon and Dirac equations. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
6. Buckled nano rod - a two state system and quantum effects on its dynamics using system plus reservoir model.
- Author
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Chakraborty, Aniruddha
- Subjects
MECHANICAL buckling ,QUANTUM theory ,NANOSTRUCTURED materials ,ELASTIC rods & wires ,POTENTIAL energy surfaces ,COMPRESSIBILITY ,HARMONIC motion ,QUANTUM tunneling - Abstract
We consider a suspended elastic rod under longitudinal compression. The compression can be used to adjust potential energy for transverse displacements from harmonic to double well regime. As compressional strain is increased to the buckling instability, the frequency of the fundamental vibrational mode drops continuously to zero (first buckling instability). As one tunes the separation between the ends of a rod, the system remains stable beyond the instability and develops a double-well potential for transverse motion. The two minima in the potential energy curve describe two possible buckled states at a particular strain. From one buckled state it can go over to the other by thermal fluctuations or quantum tunnelling. Using a continuum approach and transition state theory (TST) one can calculate the rate of conversion from one state to the other. The saddle point for the change from one state to the other is the straight rod configuration. The rate, however, diverges at the second buckling instability. At this point, the straight rod configuration, which was a saddle until then, becomes a hill top and two new saddles are generated. The new saddles have bent configurations and as the rod goes through further instabilities, they remain stable and the rate calculated according to harmonic approximation around a saddle point remains finite. In our earlier paper, a classical rate calculation including friction was carried out [J. Comput. Theor. Nanosci. 4, 1 (2007)], by assuming that each segment of the rod is coupled to its own collection of harmonic oscillators - our rate expression is well behaved through the second buckling instability. In this paper we have extended our method to calculate quantum rate using the same system plus reservoir model. We find that friction lowers the rate of conversion. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
7. Discrete binning: correspondence limit consistent analysis of classical probabilities using faux angular momenta and multi-polar harmonic moments to give 'quantum-like' probabilities.
- Author
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Anderson, Roger W.
- Subjects
PROBABILITY theory ,ANGULAR momentum (Mechanics) ,HARMONIC analysis (Mathematics) ,ENERGY storage ,ENERGY transfer ,QUANTUM theory ,DISTRIBUTION (Probability theory) ,CORRESPONDENCE analysis (Statistics) - Abstract
This paper develops discrete binning (DB) for Ni slices for classical probability functions for an arbitrary number of classical continuous variables, xi, where 0 ≤ xi ≤ 1 or -1 ≤ xi ≤ 1. Faux angular momenta, ji, are introduced where 2ji + 1 = Ni, and the discrete probabilities for the various |jimi〉 are calculated with a generalisation of the theory of Anderson and Aquilanti. Discrete probabilities are calculated from Legendre moments of the classical intensities with Clebsch-Gordan moments. The mi may represent vibrational quanta, rotational angular momenta, or discrete values of the impact parameter, scattering angles and other variables. DB directly yields probabilities for different mi, but in the correspondence limit (large ji) the discrete probabilities correspond to classical probabilities, I({xmi}), at known discrete values {xmi}. DB probabilities sum to unity, but some may be negative. Since the Clebsch-Gordan coefficients appropriate for this work are actually Gram (discrete Chebyshev) polynomials, DB is equivalent to compression and/or smoothing of data using Gram polynomials. For large Ni, DB and histogram binning (HB) provide equivalent probabilities and statistical errors. However, smoothing can often reduce the statistical errors for DB probabilities. DB is related to Legendre moment binning (LMB), but DB guides the most consistent implementation of LMB. The rule of three is introduced to provide finer resolution for DB, HB, and LMB analysis. This also leads to fractional slice binning (FSB), which is equivalent to Gaussian binning. The paper presents one-, two-, and three-dimensional examples, and spectroscopic plots are very useful for summarising the results. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
8. Ab initio potential energy curve for the neon atom pair and thermophysical properties of the dilute neon gas. I. Neon-neon interatomic potential and rovibrational spectra.
- Author
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Hellmann, Robert, Bich, Eckard, and Vogel, Eckhard
- Subjects
POTENTIAL energy surfaces ,NEON ,THERMOPHYSICAL properties ,KINETIC theory of matter ,QUANTUM theory - Abstract
A neon-neon interatomic potential energy curve was derived from quantum-mechanical ab initio calculations using basis sets of up to t-aug-cc-pV6Z quality supplemented with bond functions and ab initio methods up to CCSDT(Q). In addition, corrections for relativistic effects were determined. An analytical potential function was fitted to the ab initio values and utilised to calculate the rovibrational spectra. The quality of the interatomic potential function was tested by comparison of the calculated spectra with experimental ones and those derived from other potentials of the literature. In a following paper the new interatomic potential is applied in the framework of the quantum-statistical mechanics and of the corresponding kinetic theory to determine selected thermophysical properties of neon governed by two-body and three-body interactions. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
9. Interacting quantum trajectories for particles with spin 1/2.
- Author
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Lombardini, R. and Poirier, B.
- Subjects
QUANTUM trajectories ,BOHMIAN mechanics ,PARTICLE spin ,MOLECULAR physics ,QUANTUM theory - Abstract
In recent decades, the de Broglie-Bohm or 'pilot wave' interpretation of quantum mechanics–especially its concept of the 'quantum trajectory'–has inspired a plethora of computational methods in molecular and chemical physics. One particularly promising subclass of such methods are the 'interacting quantum trajectory' (IQT) methods, for which an ensemble of trajectories is propagated independently of–and without any recourse to–an underlying wavefunction. In this work, an IQT version of the Pauli equation is developed–enabling spin to be incorporated into IQT theories for the first time, to the authors' knowledge. The new trajectory-based dynamical equations are then used to solve two iconic quantum problems involving spin: the 'quantum spin flipper', and the Stern-Gerlach experiment. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
10. The mean square displacement of a ballistic quantum particle.
- Author
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Bindech, O., Gatti, F., Mandal, S., Marquardt, R., Shi, L., and Tremblay, J. C.
- Subjects
DISPLACEMENT (Mechanics) ,QUANTUM theory ,QUANTUM correlations ,WAVE packets ,FOURIER transforms - Abstract
A commonly used quantum mechanical formulation of the mean square displacement $ \delta _x^2(t) $ δ x 2 (t) is based on the quantum correlation function of the position operator. While this quantity yields the classically expected result $ \delta _x^2(t)\propto t^2 $ δ x 2 (t) ∝ t 2 for a ballistic particle in the interval topology, it is found here to diverge at essentially all times, when evaluated on infinitely large rings. A somewhat different formulation of the mean square displacement in quantum mechanics was proposed in a previous work (R. Marquardt, Mol. Phys. 119, e1971315 (2021)) and yielded the result $ \delta _x^2(t)\propto t $ δ x 2 (t) ∝ t for the ballistic particle on an infinitely large ring. Here, it is shown analytically that that formulation yields $ \delta _x^2(t)\equiv 0 $ δ x 2 (t) ≡ 0 for the ballistic particle on an infinitely long interval. The two formulations define two different, topology dependent quantities that have the dimension of an area and that could in principle be determined from the same experiment, following a measurement idea proposed in the aforementioned work. That idea is critically reviewed here. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
11. Spontaneous emission from nonhermitian perspective: complex scaling of the photon coordinates.
- Author
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Šindelka, Milan and Šimsa, Daniel
- Subjects
PHOTONS ,QUANTUM theory ,QUANTUM mechanics ,PERTURBATION theory ,COORDINATES ,DECAY rates (Radioactivity) - Abstract
Spontaneous emission (SE) is usually studied within the framework of quantum dissipation theory. In this paper we pursue a different view of SE. Namely, we take advantage of Nonhermitian Quantum Mechanics (NHQM) and interpret SE as the decay of a Feshbach type resonance. Correspondingly, we aim at calculating the SE decay rate Γ (resonance width) and the associated resonance wavefunction via the complex scaling (CS) method. Standard application of CS in NHQM is based on scaling the dissociative coordinates of the system,. In the case of SE, the decay consists in emitting photons. Therefore the CS must be applied on (suitably defined) position coordinates of the photons. Feasibility of such a programme is demonstrated explicitly through choosing the adequate photon coordinates and performing CS of the photon wavefunctions in the position representation. It is anticipated in this way that CS makes the full resonance wavefunction square integrable, and enables thus the calculation of Γ by proceeding in complete analogy with the well established NHQM approaches. As an illustration, the standard Golden Rule formula for Γ is rederived from the CS nonhermitian perturbation theory. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
12. Dominique Levesque.
- Author
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Hansen, Jean-Pierre and Lynden-Bell, Ruth
- Subjects
QUANTUM theory ,DIELECTRICS ,COMPUTER simulation - Abstract
Dominique Levesque celebrates his 65th birthday on August 23, 2003, and it is most appropriate that the periodical 'Molecular Physics,' which has published many of his papers, marks the occasion by paying tribute to one of the pioneers of the application of numerical and simulation methods to Statistical Mechanics of classical and quantum fluids. Levesque was born in Angers, France and took a degree in physics at the University of Rennes, France in 1959. He then moved to Paris, France, for a Master's degree in theoretical physics. Levesque was appointed a junior researcher at the Centre National de la Recherche Scientifique in 1961, and was promoted to Directeur de Recherche in 1986. He was awarded the Silver Medal of the CNRS in 1982. An important and influential part of Levesque's work deals with polar and ionic liquids, using integral equation and computer simulation techniques. He was one of the key players in solving the problem of how to determine the dielectric properties of polar and polarizable liquids by computer simulations of periodic samples.
- Published
- 2003
- Full Text
- View/download PDF
13. Quantum dynamics simulations in an ultraslow bath using hierarchy of stochastic Schrödinger equations.
- Author
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Ke, Yaling and Zhao, Yi
- Subjects
QUANTUM theory ,SCHRODINGER equation ,RANDOM numbers ,RESISTANCE heating ,BOSONS - Abstract
The hierarchy of stochastic Schrödinger equation, previously developed under the unpolarised initial bath states, is extended in this paper for open quantum dynamics under polarised initial bath conditions. The method is proved to be a powerful tool in investigating quantum dynamics exposed to an ultraslow Ohmic bath, as in this case the hierarchical truncation level and the random sampling number can be kept at a relatively small extent. By systematically increasing the system-bath coupling strength, the symmetric Ohmic spin-boson dynamics is investigated at finite temperature, with a very small cut-off frequency. It is confirmed that the slow bath makes the system dynamics extremely sensitive to the initial bath conditions. The localisation tendency is stronger in the polarised initial bath conditions. Besides, the oscillatory coherent dynamics persists even when the system-bath coupling is very strong, in correspondence with what is found recently in the deep sub-Ohmic bath, where also the low-frequency modes dominate. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
14. The time-dependent density matrix renormalisation group method.
- Author
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Ma, Haibo, Luo, Zhen, and Yao, Yao
- Subjects
RENORMALIZATION group ,DENSITY matrices ,QUANTUM theory ,COMPUTER simulation ,EXCITON theory ,PYRAZINE derivatives - Abstract
Substantial progress of the time-dependent density matrix renormalisation group (t-DMRG) method in the recent 15 years is reviewed in this paper. By integrating the time evolution with the sweep procedures in density matrix renormalisation group (DMRG), t-DMRG provides an efficient tool for real-time simulations of the quantum dynamics for one-dimensional (1D) or quasi-1D strongly correlated systems with a large number of degrees of freedom. In the illustrative applications, the t-DMRG approach is applied to investigate the nonadiabatic processes in realistic chemical systems, including exciton dissociation and triplet fission in polymers and molecular aggregates as well as internal conversion in pyrazine molecule. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
15. Memory propagator matrix for long-time dissipative charge transfer dynamics.
- Author
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Lambert, Roberto and Makri, Nancy
- Subjects
ENERGY dissipation ,CHARGE transfer ,QUANTUM theory ,DENSITY matrices ,MATHEMATICAL models ,PATH integrals ,NUMERICAL analysis - Abstract
Iterative path integral methods provide a numerically exact approach to the dynamics of a quantum system coupled to a dissipative bath. These methods involve step-by-step propagation of a generalized multi-time reduced density matrix with a propagator that includes influence functional interactions that span the bath-induced memory length. Low-frequency baths lead to long memory that can span many time steps, necessitating the use of filtering procedures that select and store only statistically significant path segments, avoiding storage of the entire sparse propagator. The present paper further enhances the iterative path integral methodology through a deterministic procedure that identifies at the start of the calculation all memory-length path segments whose weights exceed a chosen threshold and builds the propagator matrix for use in all propagation steps. A binning procedure allows efficient pairing of path segments required in the construction of the propagator. Additional savings are achieved via a simple criterion for assessing the adequacy of a chosen path selection threshold prior to propagation. Application to a tight-binding model for charge transfer in extended systems reveals the important role of bath-induced memory on the dynamics of these systems. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
16. K -independent vibrational bases for systems with large amplitude motion.
- Author
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Wang, Xiao-Gang and Carrington Jr, Tucker
- Subjects
VIBRATIONAL spectra ,QUANTUM theory ,MATHEMATICAL singularities ,MOLECULAR dynamics ,POLYNOMIALS ,LEGENDRE'S functions ,ANGULAR momentum (Nuclear physics) - Abstract
For J > 0 calculations it would be advantageous to have a vibrational basis independent of rotational quantum numbers, but which can be applied to molecules or systems with large amplitude motion. Several authors have explored the possibility of using as bend functions (m = 0) Legendre polynomials. Their most obvious disadvantage is the existence of infinite matrix elements. Their behaviour near the θ = 0 and π singularities will also be inappropriate for some wavefunctions. In this paper, we test and analyse several rotational-index-independent vibrational bases and compare them to the standard basis of associated Legendre polynomials, , where m depends on K, the quantum number for the molecule-fixed z component of the angular momentum. We find that for three-atom systems with wavefunctions having both significant amplitude at linearity and important Θ m=odd components a Legendre basis is poor, despite the repulsive singularity at linear geometries. Similar problems occur for systems with more than three atoms. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
17. 14N pulsed nuclear quadrupole resonance. 3. Effect of a pulse train. Optimal conditions for data averaging.
- Author
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Ferrari, M., Hiblot, N., Retournard, A., and Canet, D.
- Subjects
NUCLEAR quadrupole resonance ,QUADRUPOLE moments ,NUCLEAR magnetic resonance ,NITROGEN ,QUANTUM theory ,STATISTICAL mechanics - Abstract
The calculations developed in this paper aim at determining the optimal conditions of a NQR experiment when a transition is monitored by means of a pulse train with pulses of identical duration and signal acquisition after each pulse; coherences are assumed to vanish by effective transverse relaxation prior to every new pulse. These calculations demonstrate that, as in NMR, a steady state is effectively reached for any value of the recycle time. However, by contrast with NMR, it is shown that, for optimal data averaging under steady state conditions, the recycle time T can be kept as low as possible (the only limitation is the acquisition time). Nutation curves (signal amplitude versus pulse length) calculated in the steady state case are shown to depend strongly on the ratio T/T1 (T1: longitudinal relaxation time). The signal growth as a function of T/T1under averaging of the first transients has been evaluated as well as the number of pulses necessary for reaching a steady state. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
18. Theory of forward glory scattering for chemical reactions: new derivation of a uniform semiclassical formula for the scattering amplitude.
- Author
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Connor, J. N. L.
- Subjects
SCATTERING amplitude (Physics) ,SCATTERING (Physics) ,CHEMICAL reactions ,QUANTUM theory ,POLYNOMIALS ,PHYSICS - Abstract
The theory of forward glory scattering is investigated for a state-to-state chemical reaction whose scattering amplitude can be written as a Legendre partial wave series. Legendre series occur in the exact quantum theory of reactive scattering when the initial and final helicity quantum numbers are zero, as well as in many approximate theories of chemical reactions. The starting point for the semiclassical theory is a two-dimensional integral representation for the scattering amplitude. A uniform semiclassical approximation is derived that is valid for angles both on, and off, the axial caustic associated with the glory. The derivation is the first application to a concrete problem in molecular physics of a method outlined by J. N. L. Connor and H. R. Mayne in 1979 for the uniform semiclassical evaluation of multidimensional integrals. The approach exploits the theory of singularities of differential mappings. The key step in the derivation is an exact one-to-one change of variables in the neighbourhood of the stationary phase points that locally reduce the two-dimensional phase of the integrand to a non-polynomial canonical form. The derivation complements a different semiclassical glory analysis reported in a companion paper. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
19. A non-equilibrium free energy theorem for deterministic systems.
- Author
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Evans, Denis J.
- Subjects
GIBBS' free energy ,NONEQUILIBRIUM thermodynamics ,PATH integrals ,QUANTUM theory - Abstract
Jarzynski and Crooks have recently shown that equilibrium free energy differences can be computed from non-equilibrium thermodynamic path integrals. In the present paper we give a new derivation of this extraordinary relation. Our derivation which is valid for time reversible deterministic systems highlights the close relationship between the non-equilibrium free energy theorems and the fluctuation theorem. [ABSTRACT FROM AUTHOR]
- Published
- 2003
- Full Text
- View/download PDF
20. Hybrid quantum mechanical/molecular mechanical fluctuating charge models for condensed phase simulations.
- Author
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Field, Martin J.
- Subjects
QUANTUM theory ,CONDENSED matter ,POLARIZATION (Nuclear physics) - Abstract
Hybrid quantum mechanical/molecular mechanical potentials have proved to be powerful tools for the simulation of many processes in condensed phase systems and, as a result, there is much current research into how they can be improved. An area of recent attention has been the inclusion of polarization effects on the atoms in the molecular mechanical region which have been shown to be important for the calculation of certain properties. One way to treat such effects is with a dipole polarizability model. However, an alternative and, in many ways, simpler method is available that is based upon the principle of electronegativity equalization. In this paper a number of hybrid potentials are presented that employ a fluctuating charge model and electronegativity equalization to describe the electrostatic interactions in the molecular mechanical region of the system. The models are straightforward to implement and their use is illustrated with applications to some simple solution phase systems. [ABSTRACT FROM AUTHOR]
- Published
- 1997
- Full Text
- View/download PDF
21. Determining quantum bound-state eigenvalues and eigenvectors as functions of parameters in the Hamiltonian: an efficient evolutionary approach.
- Author
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Mazziotti, David A. and Rabitz, Herschel A.
- Subjects
BOUND states ,QUANTUM theory - Abstract
This paper addresses the problem of finding the quantum bound-state energy eigenvalues and eigenvectors as functions of a set of continuous parameters characterizing a Hamiltonian. A recent paper introduced a parametric equations of motion (PEM) method for this purpose, and the present work extends the method to allow for the analysis ofa single energy level and its wavefunction. After solving the Schrodinger equation for its nth eigenvalue and eigenvector, evaluated at a reference value of the Hamiltonian's parameters, the differential equations of the single-state PEM (ss-PEM) method are used to propagate the nth energy level and its eigenfunction through the entire parameter space of the Hamiltonian. The new ss-PEM method, which reduces the number of differential equations to be solved, appears more efficient than diagonalization when the energy is sought at a moderate number of values for the parameters in the Hamiltonian. The PEM methods are extended to treat non-orthogonal basis sets that facilitate more rapid convergence of the solutions. The energy of the ss-PEM, which is always an upper bound to the true energy, is exact in the limit of a complete basis set. Connections of the method are made to linear variational calculations, Dalgarno-Lewis perturbation theory and the original PEM methods. Sets of non-orthogonal Chebyshev polynomials are employed in illustrations of the ss-PEM method to determine (a) the ground-state energy as a function of internuclear separation in the hydrogen molecular ion, and (b) the ground-state energy of two electron ions as a function of nuclear charge. The calculation withthe two-electron ions involves two parameters, the nuclear charge and a basis set parameter that influences the distribution of the nodes of the Chebyshev basis functions. Evolution of the basis set parameter to improve the energies of the ions suggests an additional application of the ss-PEM method in which quantum energies are minimized with respect to nonlinear basis set parameters. The ss-PEM method offers an effective tool for mapping the solutions of the Schro dinger equation as a function of model parameters in the Hamiltonian. [ABSTRACT FROM AUTHOR]
- Published
- 1996
- Full Text
- View/download PDF
22. Sparse adaptive basis set methods for solution of the time dependent Schrodinger equation.
- Author
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Thompson, Keiran C. and Martinez, Todd J.
- Subjects
PHYSICAL & theoretical chemistry ,QUANTUM theory ,ENCYCLOPEDIAS & dictionaries ,SIGNAL processing ,SYSTEM dynamics - Abstract
Scalable numerical solutions to the time dependent Schrodinger equation remain an outstanding goal in theoretical chemistry. Here we present a method which utilises recent breakthroughs in signal processing to consistently adapt a dictionary of basis functions to the dynamics of the system. We show that for two low-dimensional model problems the size of the basis set does not grow quickly with time and appears only weakly dependent on dimensionality. The generality of this finding remains to be seen. The method primarily uses energies and gradients of the potential, opening the possibility for its use in on-the-fly ab initio quantum wavepacket dynamics. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
23. Quantum polyhedra in LCAO MO theory.
- Author
-
Carbó-Dorca, Ramon
- Subjects
POLYHEDRA ,QUANTUM theory ,MOLECULAR orbitals ,DENSITY functionals ,PARAMETER estimation - Abstract
This paper presents the definition and characterisation of quantum molecular polyhedra. They are taken here within the description of a single molecule, using quantum molecular orbital (MO) density functions as vertices. The formalism and parameters associated to these mathematical structures are analysed. Picture Drawn by Pep Camps, Girona (2015). [ABSTRACT FROM PUBLISHER]
- Published
- 2016
- Full Text
- View/download PDF
24. Comment.
- Author
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Mills, Ian
- Subjects
QUANTUM theory ,ANGULAR momentum (Mechanics) - Abstract
Comments on the discovery of quantum mechanical form of the vibration-rotation hamiltonian. Presentation of the total angular momentum and the vibrational angular momentum operators; Simplification of the expression of hamiltonian; Contributions of physicist J.K.G. Watson in the field of physics.
- Published
- 2002
- Full Text
- View/download PDF
25. The importance of initial states in polariton simulation.
- Author
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Jun Zhang, Yong-Chen Xiong, Nan Nan, Wei Li, and Wanghuai Zhou
- Subjects
QUANTUM theory ,POLARITONS ,ENERGY policy ,PHOTONS - Abstract
Nonadiabatic simulation methods are indispensable tools to investigate the dynamical processes, including the polariton formed by the hybridisation of molecule and photon. The direct product state, say |g⊗ 〉 |0〉 (|g0〉), is a convenient choice to start the simulation, with |g- and |0-denoting the molecular and photon ground state, respectively. Here, by using exact quantum dynamics simulation, we show that the LiF molecule in a cavity can become self-excited if the simulation starts with the direct product state |g0〉, leading to a finite probability to dissociate. The physical picture behind the product state simulation is that we turn on the light-matter interaction suddenly, which causes the system to occupy the high energy states that are directly coupled with the initial state even though the total energy of the whole system is conserved. Through a time-dependent lightmatter interaction model, we show that the self-excited state will disappear if the molecule moves into the cavity more slowly, i.e. adiabatically. Our results and model highlight the importance of the initial state of polariton simulation and the direct product state is unfeasible to be the initial state to investigate the dynamics of polariton, which provides new insights into the theoretical investigation of polariton dynamics. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
26. On the utility of momentum space in the density functional theory description of the steric effect.
- Author
-
Alipour, Mojtaba and Mohajeri, Afshan
- Subjects
QUANTUM theory ,PHYSICS ,ELECTROSTATICS ,STATICS ,PHYSICAL sciences - Abstract
This paper assesses the utility of momentum space in the density-based quantification of the steric effect proposed by Liu [J. Chem. Phys. 126, 244103 (2007)], which is based on a new energy partition scheme where the total electronic energy is decomposed into contributions from three independent effects: steric, electrostatic, and the fermionic quantum. The steric energy defined in this way is repulsive, exclusive, and extensive and intrinsically linked to Bader's quantum theory of atoms in molecules. In this work, the plausibility of defining and computing steric energies using momentum densities according to this scheme is confirmed from numerical tests. Moreover, we found that the correlation between the experimental scales of the steric energies and theoretical values computed from momentum densities is even better than the same correlation with theoretical estimations obtained from position densities. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
27. The à A u state of acetylene: ungerade vibrational levels in the region 45,800–46,550 cm.
- Author
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Baraban, Joshua H., Changala, P. Bryan, Merer, Anthony J., Steeves, Adam H., Bechtel, Hans A., and Field, Robert W.
- Subjects
ACETYLENE ,VIBRATIONAL spectra ,ULTRAVIOLET spectra ,BAND gaps ,QUANTUM tunneling ,ISOMERIZATION ,QUANTUM theory - Abstract
The ungerade vibrational levels of the 1Au (S1-trans) state of C2H2 lying in the region 45,800–46,550 cm−1 have been assigned from IR–UV double resonance spectra. The aim has been to classify the complete manifold of S1-trans levels in this region, so as to facilitate the assignment of the bands of S1-cis C2H2. The rotational structure is complicated because of the overlapping of vibrational polyads with different Coriolis and Darling–Dennison parameters, but assignments have been possible with the help of predictions based on the properties of polyads at lower energy. An important result is that the analysis of the (1141, 1161) polyad determines the anharmonicity constants x 14 and x 16, which will be needed to proceed to higher energies. Some regions of impressive complexity occur. Among these is the band given by the 3361, K = 1 state at 45,945 cm−1, where a three-level interaction within the S1 state is confused by triplet perturbations. Several probable S1-cis states have been observed, including cis-62, K = 1; this vibrational level appears to show a K-staggering, of the type that arises when quantum mechanical tunnelling through the barrier to cis-trans isomerization is possible. The total number of identified cis vibrational states is now 6 out of an expected 10 up to the energies discussed in this paper. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
28. Isotope shifts and band progressions in SO2 rovibrational energy levels: using quantum theory to extract rotational constants.
- Author
-
Kumar, Praveen and Poirier, Bill
- Subjects
ISOTOPE shift ,QUANTUM theory ,ANGULAR momentum (Mechanics) ,FRONTIER orbitals ,SULFUR dioxide ,SULFUR ,QUANTUM numbers - Abstract
We report the isotope shifts of the rotational constants and vibrational band progressions of the sulfur dioxide molecule (SO), for all four stable sulfur isotopes
32 S,33 S,34 S, and36 S. These are extracted from exact quantum theoretical calculations of the SO rovibrational energy levels, as reported in Chem. Phys.450–451, 59 (2015) and Chem. Phys.461, 34 (2015) and by fitting these levels to a J-shifting (JS)-type scheme, applied to a representative set of total angular momentum (J) values. The approach used to obtain the rotational constants is unusual in that it is derived directly from the quantum theoretical framework used for the earlier calculation, which gives rise to a flexible (i.e., vibrational- and rotational-state-dependent) but symmetric rotor description. The usual rotational quantum numbers are thus replaced with a single body-fixed azimuthal rotation quantum number, K, with various strategies introduced a posteriori to address rotor asymmetry. The new model fits the numerically computed rovibrational levels well, over a fairly broad range of vibrational (v) and rotational (J) excitations. The computed rotational constants agree well with previously reported experimental values [J. Chem. Phys.58, 265 (1973)]. The explicitly v- and J-dependent approach used here should thus prove valuable in broader contexts—e.g., for an analysis of self-shielding in sulfur mass-independent fractionation, even though the rovibrational levels themselves exhibit mass-dependent fractionation. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
29. Free energy methods in coupled electron ion Monte Carlo.
- Author
-
Liberatore, Elisa, Morales, Miguel A., Ceperley, David M., and Pierleoni, Carlo
- Subjects
MONTE Carlo method ,GIBBS' free energy ,PHASE diagrams ,QUANTUM theory ,HIGH pressure (Science) ,HYDROGEN ,PHASE transitions - Abstract
Recent progress in simulation methodologies and in computer power allow first-principles simulations of condensed systems with Born–Oppenheimer electronic energies obtained by quantum Monte Carlo methods. Computing free energies and therefore getting a quantitative determination of phase diagrams is one step more demanding in terms of computer resources. In this paper we derive a general relation to compute the free energy of an ab initio model with Reptation Quantum Monte Carlo (RQMC) energies from the knowledge of the free energy of the same ab initio model in which the electronic energies are computed by the less demanding but less accurate Variational Monte Carlo (VMC) method. Moreover we devise a procedure to correct transition lines based on the use of the new relation. In order to illustrate the procedure, we consider the liquid–liquid phase transition in hydrogen, a first-order transition between a lower pressure, molecular and insulating phase and a higher pressure, partially dissociated and conducting phase. We provide new results along the T = 600 K isotherm across the phase transition and find good agreement between the transition pressure and specific volumes at coexistence for the model with RQMC accuracy between the prediction of our procedure and the values that can be directly inferred from the observed plateau in the pressure–volume curve along the isotherm. This work paves the way for future use of VMC in first-principles simulations of high-pressure hydrogen, an essential simplification when considering larger system sizes or quantum proton effects by Path Integral Monte Carlo methods. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
30. Confined fluids - variations on a mean spherical theme.
- Author
-
Percus, J. K.
- Subjects
THERMODYNAMIC equilibrium ,FLUIDS ,FERMIONS ,BOSONS ,DENSITY ,QUANTUM theory ,MANY-body problem - Abstract
The mean spherical model of a classical fluid in thermal equilibrium is taken as prototype for fluids defined by their distribution of point density. An external potential Boltzmann factor applied to a reference, so defined, then produces the effect of the field on the reference. In this paper, the reference distribution is required only to reproduce the singlet and pair densities of the unperturbed fluid under study. For this purpose, the distribution can be borrowed from any many-body system, classical or quantum. Major attention is paid to elementary quantum models sufficiently parametrized to, in principle, match the desired mean singlet and pair densities. Included are independent Fermion models, independent Boson models, and those with a suitably defined intermediate statistics, whose use however involves an assertion whose range of validity is not known. An example of this mixed strategy is presented. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
31. Super instruction architecture of petascale electronic structure software: the story.
- Author
-
Lotrich, V. F., Ponton, J. M., Perera, A. S., Deumens, E., Bartlett, R. J., and Sanders, B. A.
- Subjects
ELECTRONIC structure ,SOLID state physics ,ALGORITHMS ,WAVE functions ,QUANTUM theory ,PARALLEL programming ,PHYSICS projects - Abstract
Theoretical methods in chemistry lead to algorithms for the computation of electronic energies and other properties of electronic wave functions that require large numbers of floating point operations and involve large data sets. Thus, computational chemists are very interested in using massively parallel computer systems and in particular the new petascale systems. In this paper we discuss a new programming paradigm that was developed at the Quantum Theory Project to construct electronic structure software that can scale to large numbers of cores of the order of 100,000 and beyond to solve problems in materials engineering relevant to the problems facing society today. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
32. Dynamics of electrons and nuclei.
- Author
-
Deumens, Erik and Ohrn, Yngve
- Subjects
ELECTRONIC structure ,NUCLEAR physics ,PHASE transitions ,MOLECULAR dynamics ,QUANTUM theory ,BORN-Oppenheimer approximation ,SUPERPOSITION principle (Physics) - Abstract
This paper presents the theory of Electron Nuclear Dynamics (END), which was developed and applied over the past 20 years or so in collaboration with a group of talented graduate students and postdoctoral associates. The Introduction presents the gist of this theoretical and computational approach to the study of molecular transformations. The next section outlines the major achievements of this time-dependent, direct, and non-adiabatic theory to the study of chemical change. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
33. Multi-reference many-body perturbation theory and coupled cluster developments.
- Author
-
Meissner, L.
- Subjects
MANY-body problem ,QUANTUM perturbations ,NUMERICAL analysis ,ENERGY levels (Quantum mechanics) ,ELECTRONIC excitation ,QUANTUM theory ,PHYSICS projects ,PARTITIONS (Mathematics) - Abstract
Multi-reference methods for the description of quasi-degenerate ground states and excited states of many-electron systems have been one of the main objectives of scientific activity at the Quantum Theory Project (QTP) University of Florida in Gainesville. The pioneering works by Dr. Per-Olov Lowdin on the partitioning technique, and important contributions to the development of multi-reference methods made by Dr. Monkhorst and Dr. Bartlett must be mentioned here. Dr. Bartlett, his group and its visitors have been especially active in this field. In this paper we describe some of the multi-reference developments, problems that have been faced and solved as well as those which still require solving. The focus is on multi-reference many-body perturbation theory and coupled-cluster approaches. We present recent advances and future perspectives in the development of these methods. Special attention is paid to two multi-reference approaches that seem very promising and have been either initiated or developed at QTP. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
34. QTP in the 60s: John C. Slater and the beginnings of density functional theory.
- Author
-
Connolly, John W. D.
- Subjects
QUANTUM theory ,PHYSICS projects ,DENSITY functionals ,APPROXIMATION theory ,ALPHA rays ,COMPUTER simulation - Abstract
The contributions of John C. Slater and his students to the development of quantum theory of molecules and solids have often been overlooked, especially in the area of the early computer calculations using approximations which were the predecessor to Density Functional Theory. This paper looks back to the early days of the Quantum Theory Project, when Professor Slater was heavily involved, and acknowledges research in this area which laid the foundations to the theory which has become one of the premier approximations in quantum theory today. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
35. Working at the interface.
- Author
-
Cheng, Hai-Ping
- Subjects
INTERFACES (Physical sciences) ,QUANTUM theory ,PHYSICS projects ,ENERGY levels (Quantum mechanics) ,SOLID state physics ,ELECTRON transport ,SILICA ,MOLECULAR electronics - Abstract
In this paper, a few problems based on my work at QTP are selected and organized with a focus on physical systems and processes that involve interaction between extended states in solids and localized states in molecules. Such interactions are ubiquitous in interfacial processes that stir an intense interest in the science community. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
36. Ab initio potential energy curve for the helium atom pair and thermophysical properties of dilute helium gas. I. Helium-helium interatomic potential.
- Author
-
Hellmann, Robert, Bich, Eckard, and Vogel, Eckhard
- Subjects
ELECTRONIC structure ,ENERGY-band theory of solids ,QUANTUM chemistry ,PHYSICAL & theoretical chemistry ,QUANTUM theory ,STATISTICAL mechanics - Abstract
A helium-helium interatomic potential energy curve was determined from quantum-mechanical ab initio calculations. Very large atom-centred basis sets including a newly developed d-aug-cc-pV8Z basis set supplemented with bond functions and ab initio methods up to full CI were applied. The aug-cc-pV7Z basis set of Gdanitz (J. Chem. Phys. 113, 5145 (2000)) was modified to be more consistent with the aug-cc-pV5Z and aug-cc-pV6Z basis sets. The diagonal Born-Oppenheimer corrections as well as corrections for relativistic effects were also calculated. A new analytical representation of the interatomic potential energy was fitted to the ab initio calculated values. In a following paper this potential model will be used in the framework of quantum-statistical mechanics and of the corresponding kinetic theory to calculate the most important thermophysical properties of helium governed by two-body and three-body interactions. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
37. A mathematical and computational review of Hartree-Fock SCF methods in quantum chemistry.
- Author
-
Echenique, Pablo and Alonso, J. L.
- Subjects
QUANTUM theory ,MOLECULAR orbitals ,ELECTRONIC structure ,ENERGY-band theory of solids ,PHYSICAL & theoretical chemistry ,QUANTUM chemistry - Abstract
We present a review of the fundamental topics of Hartree-Fock theory in quantum chemistry. From the molecular Hamiltonian, using and discussing the Born-Oppenheimer approximation, we arrive at the Hartree and Hartree-Fock equations for the electronic problem. Special emphasis is placed on the most relevant mathematical aspects of the theoretical derivation of the final equations, and on the results regarding the existence and uniqueness of their solutions. All Hartree-Fock versions with different spin restrictions are systematically extracted from the general case, thus providing a unifying framework. The discretization of the one-electron orbital space is then reviewed and the Roothaan-Hall formalism introduced. This leads to an exposition of the basic underlying concepts related to the construction and selection of Gaussian basis sets, focusing on algorithmic efficiency issues. Finally, we close the review with a section in which the most relevant modern developments (especially those related to the design of linear-scaling methods) are commented on and linked to the issues discussed. The paper is intentionally introductory and rather self-contained, and may be useful for non-experts intending to use quantum chemical methods in interdisciplinary applications. Moreover, much material that can be found scattered in the literature has been put together to facilitate comprehension and to serve as a handy reference. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
38. Asymptotic energy levels of a rigid asymmetric top†.
- Author
-
Watson, James K. G.
- Subjects
ENERGY levels (Quantum mechanics) ,QUANTUM theory ,RYDBERG states ,MOLECULAR spectra ,SPECTRUM analysis - Abstract
The spectra of larger molecules are often observed to high rotational quantum numbers, and the asymptotic behaviour of the rotational energy levels is of interest. This paper is mainly concerned with the lowest-energy levels for high values of J. These tend to occur in oblate-type doublets, for which E. K. Gora gave an energy-level formula in 1965 that seems to be little known among pure rotational spectroscopists. In particular, the mean energies and splittings of these doublets are discussed and a new derivation of Gora's formula is described. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
39. S matrix poles and the second virial coefficient.
- Author
-
Amaya-Tapia, A., Larsen, S. Y., Baxter, J., Lassaut, M., and Berrondo, Manuel
- Subjects
MATRICES (Mathematics) ,QUANTUM theory - Abstract
For cutoff potentials, a condition which is not a limitation for the calculation of physical systems, the S matrix is meromorphic. It may be expressed in terms of its poles, and then the quantum mechanical second virial coefficient of a neutral gas may be calculated. This paper takes another look at this approach, and discusses the feasibility, attraction and problems of the method. Among concerns are the rate of convergence of the 'pole' expansion and the physical significance of the 'higher' poles. [ABSTRACT FROM AUTHOR]
- Published
- 2002
- Full Text
- View/download PDF
40. On the calculation of the static structure factor of path-integral quantum simple fluids far from exchange.
- Author
-
Sesé, Luis M.
- Subjects
QUANTUM theory ,STATICS - Abstract
This paper addresses several points of interest concerning the computation of the static structure factor of path-integral monatomic quantum fluids. First of all, the connection between the structure factor and the path-integral linear response pair radial correlation function is shown as its defining quantity by assuming a generalized Fermi's potential for the neutron- nuclei interactions, which is to be included in the general expression of the dynamic structure factor. Second, the possibilities of finding Ornstein-Zernike equations for full path-integral fluids, and also for the effective potential models of fluids derived from the path-integral formalism, are explored by working in the grand canonical ensemble. By so doing, the success and features for improvement of the weak-field approach used previously in this context of determining quantum static structure factors [SESE,L.M.,1996, Molec. Phys., 89, 1783; SESE, L.M., and LEDESMA,R., 1997, J. chem. Phys., 106, 1134] can be understood. New numerical applications are performed within this weak-field approach taking as probes the quantum hard-sphere fluid and dense fluid helium-4, the latter being described through LennardJones and Aziz-Slaman underlying interactions. The results show that the structure factors associated with the linear response and instantaneous path-integral pair radial correlation functions differ noticeably from each other with increasing quantum effects. In particular, the linear response description leads to more compressible fluids than the instantaneous one. Besides, the equality between the isothermal compressibilities fixed via the linear response and the quantum particle centre-of-gravity pair radial correlation functions does not hold beyond the situations that can be treated with the Gaussian Feynman-Hibbs effective potential picture. Comparison with experiment in the case of helium-4 (T = 4.2 K) reveals clearly that, under strong quantum conditions, an operative framework more elaborate than the weak-field approach is needed. [ABSTRACT FROM AUTHOR]
- Published
- 2001
- Full Text
- View/download PDF
41. Implications of causality for quantum biology - I: topology change.
- Author
-
Scofield, D. F. and Collins, T. C.
- Subjects
QUANTUM theory ,QUANTUM biochemistry ,MOMENTUM (Mechanics) ,HOHENBERG-Kohn theorem ,SECOND law of thermodynamics - Abstract
A framework for describing the causal, topology changing, evolution of interacting biomolecules is developed. The quantum dynamical manifold equations (QDMEs) derived from this framework can be related to the causality restrictions implied by a finite speed of light and to Planck's constant to set a transition frequency scale. The QDMEs imply conserved stress-energy, angular-momentum and Noether currents. The functional whose extremisation leads to this result provides a causal, time-dependent, non-equilibrium generalisation of the Hohenberg-Kohn theorem. The system of dynamical equations derived from this functional and the currents
J derived from the QDMEs are shown to be causal and consistent with the first and second laws of thermodynamics. This has the potential of allowing living systems to be quantum mechanically distinguished from non-living ones. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
42. Wave vector, local momentum and local coordinate from the perspective of information theory.
- Author
-
Alipour, Mojtaba
- Subjects
WAVES (Physics) ,INFORMATION theory ,QUANTUM theory ,ENERGY density ,FISHER information ,MOMENTUM (Mechanics) - Abstract
In the context of informational analysis of atomic and molecular systems, the connection between local quantum observables and information measures is of interest. In this paper, analytical relationships for the imaginary part of the total local momentum (coordinate) in terms of information theoretic measures have been established. Moreover, on the basis of another scheme in which the relationship among densities of information energy, Shannon entropy and Fisher information has been proposed [M. Alipour and A. Mohajeri, Mol. Phys.110, 403 (2012)], the general formulae for the imaginary part of the total local momentum and the corresponding variance are expressed. The presented proof may be viewed in light of the relation between the local wave vector and the information energy density. Through this study, another noteworthy application of information theory is highlighted. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
43. Effective hamiltonian of crystal field method for periodic systems containing transition metals.
- Author
-
Popov, Ilya, Plekhanov, Evgeny, Tchougréeff, Andrei, and Besley, Elena
- Subjects
TRANSITION metals ,PHONONIC crystals ,GREEN'S functions ,SOLID state chemistry ,QUANTUM theory ,ATOMIC orbitals ,TRANSITION metal oxides - Abstract
Effective Hamiltonian of Crystal Field (EHCF) is a hybrid quantum chemical method originally developed for an accurate treatment of highly correlated d-shells in molecular complexes of transition metals. In the present work, we generalise the EHCF method to periodic systems containing transition metal atoms with isolated d-shells, either as a part of their crystal structure or as point defects. A general solution is achieved by expressing the effective resonance interactions of an isolated d-shell with the band structure of the crystal in terms of the Green's functions represented in the basis of local atomic orbitals. Such representation can be obtained for perfect crystals and for periodic systems containing atomic scale defects. Our test results for transition metal oxides (MnO, FeO, CoO, and NiO) and MgO periodic solid containing transition metal impurities demonstrate the ability of the EHCF method to accurately reproduce the spin multiplicity and spatial symmetry of the ground state. For the studied materials, these results are in a good agreement with experimentally observed d-d transitions in optical spectra. The proposed method is discussed in the context of modern solid state quantum chemistry and physics. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
44. Announcement of the winner of the Longuet–Higgins Early Career Researcher Prize 2016.
- Author
-
Jackson, George
- Subjects
SCIENTISTS ,MOLECULAR dynamics ,QUANTUM theory ,AWARDS - Published
- 2017
- Full Text
- View/download PDF
45. Note from the editor.
- Author
-
Bartlett, Rod
- Subjects
ELECTRONIC structure ,BIOLOGICAL systems ,MOLECULAR physics ,MEETINGS ,QUANTUM theory ,CONFERENCES & conventions - Published
- 2014
- Full Text
- View/download PDF
46. Quantum characteristics of the hydrogen bond.
- Author
-
Schmidt, P.P.
- Subjects
- *
QUANTUM theory , *HYDROGEN bonding , *SPECTRUM analysis , *POTENTIAL energy , *APPROXIMATION theory , *COMPRESSION loads - Abstract
Most analyses of hydrogen bond strengths and dynamics (e.g. vibrational spectroscopy and transport) have been considered in terms of (model) potential energy functions defined at the Born–Oppenheimer level of approximation. This paper reports an analysis of the quantum dynamics of hydrogen in the bond that focuses on the quantum ground state of the binding hydrogen in the fields of the other atoms. In view of its mass and size, hydrogen is delocalized in its bond much as is the electron in a covalent bond. It is shown, under certain circumstances, that the compression of the A–B distance, with hydrogen in the A–H–B bond space, yields a flatter effective A–B bond potential due to the reduction of hydrogen density along the direct AB bond line. The quantum behaviour of bonding hydrogen also influences dynamical processes such as vibrational spectroscopy and hydrogen or proton transport.†Also Adjunct Professor, Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS B3H 3J5 Canada. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
47. Electron impact total and ionization cross-sections for DNA based compounds.
- Author
-
Vinodkumar, Minaxi and Limbachiya, Chetan
- Subjects
- *
ELECTRON impact ionization , *NUCLEAR cross sections , *ELASTICITY , *URACIL , *NUCLEAR optical potentials , *DNA , *QUANTUM theory - Abstract
This paper reports computational results of the total (complete) and total ionization cross- sections, for electron impact on Uracil (C4H4N2O2) and PO3OH for impact energies from the ionization threshold to 2 keV. The total cross-section is evaluated using quantum mechanical approach using Spherical Complex Optical Potential (SCOP) presented as sum of the elastic and inelastic cross-sections. The ionization cross-sections are extracted from total inelastic cross-section using Complex Optical Potential–ionization contribution (CSP-ic) method. The present results are, in general, found to be in good agreement with previous theoretical results. In absence of any theoretical or experimental data, present results for PO3OH will serve to fill the void in the data base and may also inspire the experimentalists for some measurements as it is very important target. [ABSTRACT FROM PUBLISHER]
- Published
- 2013
- Full Text
- View/download PDF
48. Line mixing in the water vapour transitions of the ν 1 + ν 2 + ν 3 band perturbed by helium pressure.
- Author
-
Petrova, T.M., Solodov, A.M., and Solodov, A.A.
- Subjects
WATER vapor ,HELIUM ,QUANTUM theory ,WATER ,TEMPERATURE effect ,PRESSURE ,OPTICAL resolution - Abstract
The line mixing effect for two pairs of transitions with rotational quantum numbers (3 1 2) ← (4 1 3), (3 2 1) ← (4 2 2), (4 3 1) ← (3 3 0) and (4 2 2) ← (3 2 1) in the ν1 + ν2 + ν3 band of H2O has been studied. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm−1 and in a wide pressure range of helium. Pressure-broadening and -shifting coefficients and mixing parameter were obtained with help of the line profile using the Rosenkranz first-order approximation. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
- Full Text
- View/download PDF
49. Electronic structure of tris(2-phenylpyridine)iridium: electronically excited and ionized states.
- Author
-
Fine, J., Diri, K., Krylov, A.I., Nemirow, C., Lu, Z., and Wittig, C.
- Subjects
ELECTRONIC structure ,IRIDIUM ,PYRIDINE ,EXCITED state chemistry ,IONIZATION (Atomic physics) ,TRANSITION metal complexes ,QUANTUM theory ,LIGHT emitting diodes ,DENSITY functionals - Abstract
A computational study of tris(2-phenylpyridine)iridium, Ir(ppy)3, is presented. The perspective is that of using organo-transition-metal complexes as phosphorescent species in light-emitting diodes (OLED's). Quantum yields approaching 100% are possible through a triplet harvesting mechanism. Complexes such as Ir(ppy)3 are amenable to exacting experimental and theoretical studies: small enough to accommodate rigor, yet large enough to support bulk phenomena in a range of host materials. The facial and meridional isomers differ by ∼220 meV, with fac-Ir(ppy)3 having the lower energy. Because fac-Ir(ppy)3 dominates in most environments, focus is on this species. Time-dependent density functional theory using long-range-corrected functionals (BNL and ωB97X) is used to calculate excited states of Ir(ppy)3 and a few low energy states of . The calculated T1 – S0 energy gap (2.30 eV) is in reasonable agreement with the experimental value of 2.44 eV. Only a few percent of singlet character in T1 is needed to explain so short a phosphorescence lifetime as 200 ns, because of the large and absorption cross-sections. Equilibrium geometries are calculated for S0, T1, and the lowest cation state (D0), and several ionization energies are obtained: adiabatic (5.86 eV); vertical from the S0 equilibrium geometry (5.88 eV); and vertical ionization of T1 at its equilibrium geometry (5.87 eV). These agree with a calculation by Hay (5.94 eV), and with the conservative experimental upper bound of 6.4 eV. Molecular orbitals provide qualitative explanations. A calculated UV absorption spectrum, in which transitions are vertical from the S0 equilibrium geometry, agrees with the room temperature experimental spectrum. This is consistent with Franck–Condon factors dominated by , as expected given the delocalized nature of the orbitals. Ir(ppy)3 vibrational frequencies were calculated and used to estimate the probability density for 500 K, i.e. the temperature at which the experiments were carried out. In combination with the vibrational energy imparted through photoexcitation, it is seen that a large amount of vibrational energy appears in without causing its fragmentation. Specifically, for = 15,000 cm−1, the probability density for total vibrational energy peaks at ∼31,000 cm−1 with a 7800 cm−1 width. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
50. Dynamics of electron transfer in complex glassy environment modeled by the Cole–Davidson spectral density.
- Author
-
Zhou, Yun, Shao, Jiushu, and Wang, Haobin
- Subjects
CHARGE exchange ,COMPLEXITY (Philosophy) ,QUANTUM theory ,VARIATIONAL principles ,PARAMETER estimation ,APPROXIMATION theory ,MATHEMATICAL models - Abstract
The dynamics of electron transfer reactions in a complex environment is investigated in the context of the spin-boson model with a bath characterized by the Cole–Davidson spectral density. Using the numerically exact multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) method, the population dynamics of the two-level subsystem has been investigated in a broad physical regime. Upon changing various parameters, the simulation results exhibit either weakly damped coherent motion, incoherent decay, or localization. Transitions between these regimes are discussed in terms of several important physical parameters. Comparison of the exact ML-MCTDH simulations with the non-interacting blip approximation (NIBA) shows that the latter performs quite well in the nonadiabatic regime despite the complex multiple time scales the bath exhibits, but fails in the adiabatic and intermediate regimes where the relaxation of the bath is no longer significantly faster than the electron transfer process. In the nonadiabatic regime an interesting, semi-quantitative finding on electron transfer dynamics is discussed based on a simple relation between two parameters in the Cole–Davidson spectral density, the coupling strength and the fractional stretching exponent. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
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