182 results
Search Results
2. Efficient and improved prediction of the band offsets at semiconductor heterojunctions from meta-GGA density functionals: A benchmark study.
- Author
-
Ghosh, Arghya, Jana, Subrata, Rauch, Tomáš, Tran, Fabien, Marques, Miguel A. L., Botti, Silvana, Constantin, Lucian A., Niranjan, Manish K., and Samal, Prasanjit
- Subjects
DENSITY functionals ,IONIZATION energy ,SEMICONDUCTOR junctions ,SEMICONDUCTORS ,ELECTRON affinity ,HETEROJUNCTIONS ,KINETIC energy - Abstract
Accurate theoretical prediction of the band offsets at interfaces of semiconductor heterostructures can often be quite challenging. Although density functional theory has been reasonably successful to carry out such calculations, efficient, accurate semilocal functionals are desirable to reduce the computational cost. In general, the semilocal functionals based on the generalized gradient approximation (GGA) significantly underestimate the bulk bandgaps. This, in turn, results in inaccurate estimates of the band offsets at the heterointerfaces. In this paper, we investigate the performance of several advanced meta-GGA functionals in the computational prediction of band offsets at semiconductor heterojunctions. In particular, we investigate the performance of r
2 SCAN (two times revised strongly constrained and appropriately normed functional), rMGGAC (revised semilocal functional based on cuspless hydrogen model and Pauli kinetic energy density functional), mTASK (modified Aschebrock and Kümmel meta-GGA functional), and local modified Becke–Johnson exchange-correlation functionals. Our results strongly suggest that these meta-GGA functionals for supercell calculations perform quite well, especially, when compared to computationally more demanding GW calculations. We also present band offsets calculated using ionization potentials and electron affinities, as well as band alignment via the branch point energies. Overall, our study shows that the aforementioned meta-GGA functionals can be used within the density functional theory framework to estimate the band offsets in semiconductor heterostructures with predictive accuracy. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
3. Reworking the Tao–Mo exchange-correlation functional. I. Reconsideration and simplification.
- Author
-
Francisco, H., Cancio, A. C., and Trickey, S. B.
- Subjects
- *
THERMOCHEMISTRY , *KINETIC energy , *PERFORMANCE standards , *INVESTIGATION reports , *ENERGY density - Abstract
The revised, regularized Tao–Mo (rregTM) exchange-correlation density functional approximation (DFA) [A. Patra, S. Jana, and P. Samal, J. Chem. Phys. 153, 184112 (2020) and Jana et al., J. Chem. Phys. 155, 024103 (2021)] resolves the order-of-limits problem in the original TM formulation while preserving its valuable essential behaviors. Those include performance on standard thermochemistry and solid data sets that is competitive with that of the most widely explored meta-generalized-gradient-approximation DFAs (SCAN and r2SCAN) while also providing superior performance on elemental solid magnetization. Puzzlingly however, rregTM proved to be intractable for de-orbitalization via the approach of Mejía-Rodríguez and Trickey [Phys. Rev. A 96, 052512 (2017)]. We report investigation that leads to diagnosis of how the regularization in rregTM of the z indicator functions (z = the ratio of the von-Weizsäcker and Kohn–Sham kinetic energy densities) leads to non-physical behavior. We propose a simpler regularization that eliminates those oddities and that can be calibrated to reproduce the good error patterns of rregTM. We denote this version as simplified, regularized Tao–Mo, sregTM. We also show that it is unnecessary to use rregTM correlation with sregTM exchange: Perdew–Burke–Ernzerhof correlation is sufficient. The subsequent paper shows how sregTM enables some progress on de-orbitalization. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
4. Towards a systematic way to correct density functional approximations.
- Author
-
Savin, Andreas
- Subjects
DENSITY functional theory ,WAVE functions ,KINETIC energy ,SCHRODINGER equation ,HAMILTONIAN operator - Abstract
In order to simulate the exact universal density functional, approximations are nowadays constructed by permitting more flexibility in its ansatz. In view of the difficulty of defining a systematically improvable form for it, this paper argues that an alternative way could be considered. It falls within the class of hybrid functionals with multi-determinant wave functions. The parameter controlling the hybridization is considered as variable. The invariance of the exact result with respect to changes in this variable is used to introduce information about the system under consideration, and to correct the density functional result. The construction considered in this paper accelerates convergence from the model system to the physical one, in the vicinity of the latter. The method, at the present level of implementation, should be seen as a starting point for further development, and not necessarily as a computationally advantageous tool. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
5. A multi-dimensional Smolyak collocation method in curvilinear coordinates for computing vibrational spectra.
- Author
-
Avila, Gustavo and Carrington, Tucker
- Subjects
VIBRATIONAL spectra ,KINETIC energy ,DIFFERENTIAL operators ,ENERGY levels (Quantum mechanics) ,CURVILINEAR coordinates ,COMPUTER systems - Abstract
In this paper, we improve the collocation method for computing vibrational spectra that was presented in Avila and Carrington, Jr. [J. Chem. Phys. 139, 134114 (2013)]. Using an iterative eigensolver, energy levels and wavefunctions are determined from values of the potential on a Smolyak grid. The kinetic energy matrix-vector product is evaluated by transforming a vector labelled with (nondirect product) grid indices to a vector labelled by (nondirect product) basis indices. Both the transformation and application of the kinetic energy operator (KEO) scale favorably. Collocation facilitates dealing with complicated KEOs because it obviates the need to calculate integrals of coordinate dependent coefficients of differential operators. The ideas are tested by computing energy levels of HONO using a KEO in bond coordinates. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
6. Neural network learned Pauli potential for the advancement of orbital-free density functional theory.
- Author
-
Gangwar, Aparna, Bulusu, Satya S., and Banerjee, Arup
- Subjects
- *
DENSITY functional theory , *DENSITY functionals , *KINETIC energy , *EULER equations , *ELECTRONIC structure - Abstract
The Pauli kinetic energy functional and its functional derivative, termed Pauli potential, play a crucial role in the successful implementation of orbital-free density functional theory for electronic structure calculations. However, the exact forms of these two quantities are not known. Therefore, perforce, one employs the approximate forms for the Pauli functional or Pauli potential for performing orbital-free density functional calculations. In the present study, we developed a feed-forward neural network-based representation for the Pauli potential using a 1-dimensional (1-D) model system. We expanded density in terms of basis functions, and the coefficients of the expansion were used as input to a feed-forward neural network. Using the neural network-based representation of the Pauli potential, we calculated the ground-state densities of the 1-D model system by solving the Euler equation. We calculated the Pauli kinetic energy using the neural network-based Pauli potential employing the exact relation between the Pauli kinetic energy functional and the potential. The sum of the neural network-based Pauli kinetic energy and the von Weizsäcker kinetic energy resulted in an accurate estimation of the total kinetic energy. The approach presented in this paper can be employed for the calculation of Pauli potential and Pauli kinetic energy, obviating the need for a functional derivative. The present study is an important step in the advancement of application of machine learning-based techniques toward the orbital-free density functional theory-based methods. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
7. A study of accurate exchange-correlation functionals through adiabatic connection.
- Author
-
Singh, Rabeet and Harbola, Manoj K.
- Subjects
ADIABATIC processes ,ENERGY function ,DENSITY functional theory ,ELECTRONS ,KINETIC energy - Abstract
A systematic way of improving exchange-correlation energy functionals of density functional theory has been to make them satisfy more and more exact relations. Starting from the initial generalized gradient approximation (GGA) functionals, this has culminated into the recently proposed SCAN (strongly constrained and appropriately normed) functional that satisfies several known constraints and is appropriately normed. The ultimate test for the functionals developed is the accuracy of energy calculated by employing them. In this paper, we test these exchange-correlation functionals--the GGA hybrid functionals B3LYP and PBE0 and the meta-GGA functional SCAN--from a different perspective. We study how accurately these functionals reproduce the exchange-correlation energy when electron-electron interaction is scaled as αV
ee with α varying between 0 and 1. Our study reveals interesting comparison between these functionals and the associated difference Tc between the interacting and the non-interacting kinetic energy for the same density. [ABSTRACT FROM AUTHOR]- Published
- 2017
- Full Text
- View/download PDF
8. Computing vibrational energy levels of CH4 with a Smolyak collocation method.
- Author
-
Avila, Gustavo and Carrington Jr., Tucker
- Subjects
VIBRATIONAL redistribution (Molecular physics) ,COLLOCATION methods ,KINETIC energy ,HIERARCHICAL clustering (Cluster analysis) ,UNIVARIATE analysis - Abstract
In this paper, we demonstrate that it is possible to apply collocation to compute vibrational energy levels of a five-atom molecule using an exact kinetic energy operator (with cross terms and coordinatedependent coefficients). This is made possible by using (1) a pruned basis of products of univariate functions; (2) a Smolyak grid made from nested sequences of grids for each coordinate; (3) a collocation method that obviates the need to solve a generalized eigenvalue problem; (4) an efficient sequential transformation between the (nondirect product) grid and the (nondirect product) basis representations; and (5) hierarchical univariate functions that make it possible to avoid storing large intermediate vectors. The accuracy of the method is confirmed by computing 500 vibrational energy levels of methane. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
9. Refinement of thermostated molecular dynamics using backward error analysis.
- Author
-
Silveira, Ana J. and Abreu, Charlles R. A.
- Subjects
ERROR analysis in mathematics ,MOLECULAR dynamics ,CANONICAL ensemble ,KINETIC energy ,NUMERICAL integration ,RIGID bodies - Abstract
Kinetic energy equipartition is a premise for many deterministic and stochastic molecular dynamics methods that aim at sampling a canonical ensemble. While this is expected for real systems, discretization errors introduced by the numerical integration may lead to deviations from equipartition. Fortunately, backward error analysis allows us to obtain a higher-order estimate of the quantity that is actually subject to equipartition. This is related to a shadow Hamiltonian, which converges to the specified Hamiltonian only when the time-step size approaches zero. This paper deals with discretization effects in a straightforward way. With a small computational overhead, we obtain refined versions of the kinetic and potential energies, whose sum is a suitable estimator of the shadow Hamiltonian. Then, we tune the thermostatting procedure by employing the refined kinetic energy instead of the conventional one. This procedure is shown to reproduce a canonical ensemble compatible with the refined system, as opposed to the original one, but canonical averages regarding the latter can easily be recovered by reweighting. Water, modeled as a rigid body, is an excellent test case for our proposal because its numerical stability extends up to time steps large enough to yield pronounced discretization errors in Verlet-type integrators. By applying our new approach, we were able to mitigate discretization effects in equilibrium properties of liquid water for time-step sizes up to 5 fs. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
10. Validity of virial theorem in all-electron mixed basis density functional, Hartree-Fock, and GW calculations.
- Author
-
Kuwahara, Riichi, Tadokoro, Yoichi, and Ohno, Kaoru
- Subjects
VIRIAL theorem ,DENSITY functional theory ,HARTREE-Fock approximation ,KINETIC energy ,ELECTRON energy states ,GROUND state energy - Abstract
In this paper, we calculate kinetic and potential energy contributions to the electronic ground-state total energy of several isolated atoms (He, Be, Ne, Mg, Ar, and Ca) by using the local density approximation (LDA) in density functional theory, the Hartree-Fock approximation (HFA), and the self-consistent GW approximation (GWA). To this end, we have implemented self-consistent HFA and GWA routines in our all-electron mixed basis code, TOMBO. We confirm that virial theorem is fairly well satisfied in all of these approximations, although the resulting eigenvalue of the highest occupied molecular orbital level, i.e., the negative of the ionization potential, is in excellent agreement only in the case of the GWA. We find that the wave function of the lowest unoccupied molecular orbital level of noble gas atoms is a resonating virtual bound state, and that of the GWA spreads wider than that of the LDA and thinner than that of the HFA. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
11. Computing rovibrational levels of methane with curvilinear internal vibrational coordinates and an Eckart frame.
- Author
-
Wang, Xiao-Gang and Carrington, Tucker
- Subjects
METHANE ,VIBRATION (Mechanics) ,POLYATOMIC molecules ,SCHRODINGER equation ,NUMERICAL analysis ,WAVE functions ,KINETIC energy - Abstract
We present a new procedure for computing a rovibrational spectrum of a polyatomic molecule and apply it to methane. The Schrödinger equation is solved, numerically exactly, by using a nested contracted basis. Rovibrational wavefunctions are computed in a |v>|JKM> basis, where |v> is a vibrational wavefunction and |JKM> is a symmetric top wavefunction. In turn, the |v> are obtained by solving a vibrational Schrödinger equation with basis functions that are products of contracted bend and stretch functions. At all stages of the calculation we exploit parity symmetry. The calculations are done in internal coordinates that facilitate the treatment of large amplitude motion. An Eckart molecule-fixed frame is used by numerically computing coefficients of the kinetic energy operator. The efficacy of the method is demonstrated by calculating a large number of converged J = 10 methane rovibrational levels in the Tetradecad polyad. No previous calculation of rovibrational levels of methane includes as many levels as we report in this paper. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
12. Self-consistent implementation of meta-GGA functionals for the ONETEP linear-scaling electronic structure package.
- Author
-
Womack, James C., Mardirossian, Narbe, Head-Gordon, Martin, and Skylaris, Chris-Kriton
- Subjects
DENSITY functional theory ,ELECTRONIC structure ,AMYLOID beta-protein ,KINETIC energy ,APPROXIMATION theory - Abstract
Accurate and computationally efficient exchange-correlation functionals are critical to the successful application of linear-scaling density functional theory (DFT). Local and semi-local functionals of the density are naturally compatible with linear-scaling approaches, having a general form which assumes the locality of electronic interactions and which can be efficiently evaluated by numerical quadrature. Presently, the most sophisticated and flexible semi-local functionals are members of the meta-generalized-gradient approximation (meta-GGA) family, and depend upon the kinetic energy density, τ, in addition to the charge density and its gradient. In order to extend the theoretical and computational advantages of τ-dependent meta-GGA functionals to large-scale DFT calculations on thousands of atoms, we have implemented support for τ-dependent meta-GGA functionals in the ONETEP program. In this paper we lay out the theoretical innovations necessary to implement τ-dependent meta-GGA functionals within ONETEP's linear-scaling formalism. We present expressions for the gradient of the τ-dependent exchange-correlation energy, necessary for direct energy minimization. We also derive the forms of the τ-dependent exchange-correlation potential and kinetic energy density in terms of the strictly localized, self-consistently optimized orbitals used by ONETEP. To validate the numerical accuracy of our self-consistent meta-GGA implementation, we performed calculations using the B97M-V and PKZB meta-GGAs on a variety of small molecules. Using only a minimal basis set of self-consistently optimized local orbitals, we obtain energies in excellent agreement with large basis set calculations performed using other codes. Finally, to establish the linear-scaling computational cost and applicability of our approach to large-scale calculations, we present the outcome of self-consistent meta-GGA calculations on amyloid fibrils of increasing size, up to tens of thousands of atoms. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
13. An ergodic configurational thermostat using selective control of higher order temperatures.
- Author
-
Patra, Puneet Kumar and Bhattacharya, Baidurya
- Subjects
ERGODIC theory ,THERMOSTAT ,HIGH temperatures ,DEGREES of freedom ,KINETIC energy - Abstract
The conventional Nosé-Hoover type deterministic thermostat scheme for controlling temperature by configurational variables (Braga-Travis (BT) thermostat) is non-ergodic for systems with a few degrees of freedom. While for the original Nosé-Hoover kinetic thermostat ergodicity has been achieved by controlling the higher order moments of kinetic energy, the issues of nonergodicity of BT thermostat persists. In this paper, we introduce two new measures of configurational temperature (second and third order) based on the generalized temperature-curvature relationship and obtain a family of deterministic thermostatting schemes by selectively (and simultaneously) controlling the different orders of temperatures through pseudo-friction terms. The ergodic characteristics of the proposed thermostats are tested using a single harmonic oscillator through statistical (normality of joint distributions at different Poincare sections) as well as dynamical tests (difference of the minimum and maximum largest Lyapunov exponent). Our results indicate that simultaneously controlling the first and the second order configurational temperatures (C
1,2 thermostat) is sufficient to make the dynamics ergodic. A 2000 particle Lennard-Jones system is subjected to (i) equilibrium and (ii) sudden temperature change under BT and C1,2 thermostatting schemes. The C1,2 thermostat is found to be more robust than the BT thermostat without increasing computational costs. [ABSTRACT FROM AUTHOR]- Published
- 2015
- Full Text
- View/download PDF
14. Kinetic and electron-electron energies for convex sums of ground state densities with degeneracies and fractional electron number.
- Author
-
Levy, Mel, Anderson, James S. M., Zadeh, Farnaz Heidar, and Ayers, Paul W.
- Subjects
ELECTRON-electron interactions ,DENSITY functional theory ,KINETIC energy ,HOHENBERG-Kohn theorem ,MOLECULAR shapes ,FLUORESCENCE resonance energy transfer - Abstract
Properties of exact density functionals provide useful constraints for the development of new approximate functionals. This paper focuses on convex sums of ground-level densities. It is observed that the electronic kinetic energy of a convex sum of degenerate ground-level densities is equal to the convex sum of the kinetic energies of the individual degenerate densities. (The same type of relationship holds also for the electron-electron repulsion energy.) This extends a known property of the Levy-Valone Ensemble Constrained-Search and the Lieb Legendre-Transform refomulations of the Hohenberg-Kohn functional to the individual components of the functional. Moreover, we observe that the kinetic and electron-repulsion results also apply to densities with fractional electron number (even if there are no degeneracies), and we close with an analogous point-wise property involving the external potential. Examples where different degenerate states have different kinetic energy and electron-nuclear attraction energy are given; consequently, individual components of the ground state electronic energy can change abruptly when the molecular geometry changes. These discontinuities are predicted to be ubiquitous at conical intersections, complicating the development of universally applicable density-functional approximations. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
15. Goal-oriented sensitivity analysis for lattice kinetic Monte Carlo simulations.
- Author
-
Arampatzis, Georgios and Katsoulakis, Markos A.
- Subjects
SENSITIVITY analysis ,MONTE Carlo method ,LATTICE theory ,KINETIC energy ,SIMULATION methods & models ,STOCHASTIC analysis ,HAMILTON'S equations - Abstract
In this paper we propose a new class of coupling methods for the sensitivity analysis of high dimensional stochastic systems and in particular for lattice Kinetic Monte Carlo (KMC). Sensitivity analysis for stochastic systems is typically based on approximating continuous derivatives with respect to model parameters by the mean value of samples from a finite difference scheme. Instead of using independent samples the proposed algorithm reduces the variance of the estimator by developing a strongly correlated-"coupled"- stochastic process for both the perturbed and unperturbed stochastic processes, defined in a common state space. The novelty of our construction is that the new coupled process depends on the targeted observables, e.g., coverage, Hamiltonian, spatial correlations, surface roughness, etc., hence we refer to the proposed method as goal-oriented sensitivity analysis. In particular, the rates of the coupled Continuous Time Markov Chain are obtained as solutions to a goal-oriented optimization problem, depending on the observable of interest, by considering the minimization functional of the corresponding variance. We show that this functional can be used as a diagnostic tool for the design and evaluation of different classes of couplings. Furthermore, the resulting KMC sensitivity algorithm has an easy implementation that is based on the Bortz-Kalos-Lebowitz algorithm's philosophy, where events are divided in classes depending on level sets of the observable of interest. Finally, we demonstrate in several examples including adsorption, desorption, and diffusion Kinetic Monte Carlo that for the same confidence interval and observable, the proposed goal-oriented algorithm can be two orders of magnitude faster than existing coupling algorithms for spatial KMC such as the Common Random Number approach. We also provide a complete implementation of the proposed sensitivity analysis algorithms, including various spatial KMC examples, in a supplementary MATLAB source code. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
16. Effect of laser spectral bandwidth on coherent control of resonance-enhanced multiphoton-ionization photoelectron spectroscopy.
- Author
-
Shuwu Xu, Jingxin Ding, Chenhui Lu, Tianqing Jia, Shian Zhang, and Zhenrong Sun
- Subjects
IONIZATION (Atomic physics) ,PHOTOELECTRON spectroscopy ,KINETIC energy ,EXCITATION spectrum ,LASERS - Abstract
The high-resolution (2 + 1) resonance-enhanced multiphoton-ionization photoelectron spectroscopy (REMPI-PS) can be obtained by measuring the photoelectron intensity at a given kinetic energy and scanning the single p phase step position. In this paper, we further demonstrate that the highresolution (2 + 1) REMPI-PS cannot be achieved at any measured position of the kinetic energy by this measurement method, which is affected by the laser spectral bandwidth. We propose a double p phase step modulation to eliminate the effect of the laser spectral bandwidth, and show the advantage of the double p phase step modulation on achieving the high-resolution (2 + 1) REMPI-PS by considering the contributions involving on- and near-resonant three-photon excitation pathways. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
17. Reduced dimension rovibrational variational calculations of the S1 state of C2H2. I. Methodology and implementation.
- Author
-
Changala, P. Bryan
- Subjects
PHYSICS research ,ACETYLENE ,ISOMERIZATION ,MOLECULAR vibration ,KINETIC energy ,ELECTRON kinetic energy ,INELASTIC collisions - Abstract
The bending and torsional degrees of freedom in S
1 acetylene, C2 H2 , are subject to strong vibrational resonances and rovibrational interactions, which create complex vibrational polyad structures even at low energy. As the internal energy approaches that of the barrier to cis-trans isomerization, these energy level patterns undergo further large-scale reorganization that cannot be satisfactorily treated by traditional models tied to local minima of the potential energy surface for nuclear motion. Experimental spectra in the region near the cis-trans transition state have revealed these complicated new patterns. In order to understand near-barrier spectroscopic observations and to predict the detailed effects of cis-trans isomerization on the rovibrational energy level structure, we have performed reduced dimension rovibrational variational calculations of the S1 state. In this paper, we present the methodological details, several of which require special care. Our calculation uses a high accuracy ab initio potential surface and a fully symmetrized extended complete nuclear permutation inversion group theoretical treatment of a multivalued internal coordinate system that is appropriate for large amplitude bending and torsional motions. We also discuss the details of the rovibrational basis functions and their symmetrization, as well as the use of a constrained reduced dimension rovibrational kinetic energy operator. [ABSTRACT FROM AUTHOR]- Published
- 2014
- Full Text
- View/download PDF
18. On the derivation of semiclassical expressions for quantum reaction rate constants in multidimensional systems.
- Author
-
Kryvohuz, Maksym
- Subjects
QUANTUM theory ,APPROXIMATION theory ,PATH integrals ,KINETIC energy ,DEGREES of freedom ,ZERO point energy ,TEMPERATURE effect - Abstract
Expressions for reaction rate constants in multidimensional chemical systems are derived by applying semiclassical approximation to the quantum path integrals of the ImF formulation of reaction rate theory. First, the transverse degrees of freedom orthogonal to the reaction coordinate are treated within the steepest descent approximation, after which the semiclassical approximation is applied to the remaining reaction coordinate. Thus derived, the semiclassical expressions account for the multidimensional nature of quantum effects and accurately incorporate nuclear quantum effects such as multidimensional tunneling and zero point energies. The obtained expressions are applicable in the broad temperature range from the deep tunneling to high-temperature regimes. The present paper provides derivation of the semiclassical instanton expressions proposed by Kryvohuz [J. Chem. Phys. 134, 114103 (2011)]. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
19. Regular reaction dynamics in analytical form in the vicinity of symmetrical transition states. Central barrier crossings in SN2 reactions.
- Author
-
Lorquet, J. C.
- Subjects
SPHERICAL coordinates ,POTENTIAL energy surfaces ,EQUATIONS of motion ,KINETIC energy ,TRANSITION state theory (Chemistry) ,ANHARMONIC motion - Abstract
When an activated complex, as defined in transition state theory (TST), has a polyhedral shape, its kinetic energy is found to be diagonal in a system of spherical polar coordinates. If, in addition, the polyhedron is characterized by a high symmetry, then its dynamics considerably simplifies. An application of this approach to the most symmetrical TS known to date, i.e., that which controls the Cl
− + CH3 Cl → ClCH3 + Cl− SN 2 nucleophilic substitution, is presented and an analytical expression of its potential energy surface is provided. In a substantial range around the saddle point, approximate equations of motion for the two components of the reaction coordinate, i.e., the antisymmetrical stretching motion of the ClCCl core and the wagging motion of the hydrogen triad, can be derived in an analytical form. During an extensive period of time, the main component of the reaction coordinate is governed by an unexpectedly simple equation of motion that depends on a single initial condition, irrespective of the other ones and of the internal energy. Reactive trajectories are observed to form a perfectly collimated bundle characterized by undetectable dispersion, thereby giving a spectacular example of regular dynamics in an anharmonic potential. Regularity and collimation are brought about by local symmetry, which is a widespread feature of potential energy surfaces. Anharmonicity is observed to influence the dynamics only at a late stage. As energy increases, trajectories tend to fan out and to deviate from the analytical equation. For the wagging motion, chaos sets in at much lower energies. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
20. Electron circular dichroism in hot electron emission from metallic nanohelix arrays.
- Author
-
Nürenberg, Daniel, Mark, Andrew G., Fischer, Peer, and Zacharias, Helmut
- Subjects
ELECTRON emission ,HOT carriers ,FEMTOSECOND pulses ,SILVER alloys ,KINETIC energy ,PHOTOEMISSION ,CIRCULAR dichroism - Abstract
We investigate the electron emission from 3D chiral silver alloy nanohelices initiated by femtosecond laser pulses with a central photon energy of hν = 1.65 eV, well below the work function of the material. We find hot but thermally distributed electron spectra and a strong anisotropy in the electron yield with left- and right-circularly polarized light excitations, which invert in sign between left- and right-handed helices. We analyze the kinetic energy distribution and discuss the role of effective temperatures. Measurements of the reflectance and simulations of the absorbance of the helices based on retarded field calculations are compared to the anisotropy in photoemission. We find a significant enhancement of the anisotropy in the electron emission in comparison to the optical absorption. Neither simple thermionic nor a multiphoton photoemission can explain the experimentally observed asymmetries. Single photon deep-UV photoemission from these helices together with a change of the work function suggests a contribution of the chirally induced spin selectivity effect to the observed asymmetries. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
21. Quantum evolution represented by Brownian motion.
- Author
-
Shao, Jiushu
- Subjects
QUANTUM mechanics ,SCHRODINGER equation ,KINETIC energy ,QUANTUM operators ,RANDOM noise theory ,BROWNIAN motion - Abstract
We propose a stochastic Schrödinger equation in which the momentum is coupled to a white Gaussian noise. In the stochastic representation, the kinetic energy representing the self-interaction of momentum is reduced to a linear term of momentum. As such, the quantum evolution operator factorizes into two contributions due to the momentum and the potential, respectively. The exact quantum propagator thereby becomes an expectation of the stochastic one in which the amplitude results from the potential with a fluctuating position: The particle moves with a constant velocity, subjected to a complex Brownian motion. We demonstrate that the stochastic Schrödinger equation can be feasibly used to derive the quantum propagators for the linear potential and the harmonic oscillator system. Novel semiclassical and other approximations may be developed from the new representation of quantum mechanics. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
22. CNT effective interfacial energy and pre-exponential kinetic factor from measured NaCl crystal nucleation time distributions in contracting microdroplets.
- Author
-
Cedeno, Ruel, Grossier, Romain, Candoni, Nadine, Levernier, Nicolas, Flood, Adrian E., and Veesler, Stéphane
- Subjects
MICRODROPLETS ,NUCLEATION ,KINETIC energy ,POISSON distribution ,SALT - Abstract
Nucleation, the birth of a stable cluster from a disorder, is inherently stochastic. Yet up to date, there are no quantitative studies on NaCl nucleation that accounts for its stochastic nature. Here, we report the first stochastic treatment of NaCl-water nucleation kinetics. Using a recently developed microfluidic system and evaporation model, our measured interfacial energies extracted from a modified Poisson distribution of nucleation time show an excellent agreement with theoretical predictions. Furthermore, analysis of nucleation parameters in 0.5, 1.5, and 5.5 pl microdroplets reveals an interesting interplay between confinement effects and shifting of nucleation mechanisms. Overall, our findings highlight the need to treat nucleation stochastically rather than deterministically to bridge the gap between theory and experiment. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
23. Contactium: A strongly correlated model system.
- Author
-
Cioslowski, Jerzy, Englert, Berthold-Georg, Trappe, Martin-Isbjörn, and Hue, Jun Hao
- Subjects
BOSONS ,SCHRODINGER equation ,NATURAL orbitals ,KINETIC energy ,ANGULAR momentum (Mechanics) ,ENERGY security - Abstract
At the limit of an infinite confinement strength ω, the ground state of a system that comprises two fermions or bosons in harmonic confinement interacting through the Fermi–Huang pseudopotential remains strongly correlated. A detailed analysis of the one-particle description of this "contactium" reveals several peculiarities that are not encountered in conventional model systems (such as the two-electron harmonium atom, ballium, and spherium) involving Coulombic interparticle interactions. First of all, none of the natural orbitals (NOs) { ψ n (ω ; r) } of the contactium is unoccupied, which implies nonzero collective occupancies for all the angular momenta. Second, the NOs and their non-ascendingly ordered occupation numbers { ν n } turn out to be related to the eigenfunctions and eigenvalues of a zero-energy Schrödinger equation with an attractive Gaussian potential. This observation enables the derivation of their properties, such as the n − 4 / 3 asymptotic decay of ν n at the n → ∞ limit (which differs from that of n − 8 / 3 in the Coulombic systems), the independence of the confinement energy v n = ⟨ ψ n (ω ; r) | 1 2 ω 2 r 2 | ψ n (ω ; r) ⟩ of n , and the n − 2 / 3 asymptotic decay of the respective contribution ν n t n to the kinetic energy. Upon suitable scaling, the weakly occupied NOs of the contactium turn out to be virtually identical to those of the two-electron harmonium atom at the ω → ∞ limit, despite the entirely different interparticle interactions in these systems. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
24. Energy response and spatial alignment of the perturbed electron gas.
- Author
-
Dornheim, Tobias, Tolias, Panagiotis, Moldabekov, Zhandos A., and Vorberger, Jan
- Subjects
WAVENUMBER ,PATH integrals ,POTENTIAL energy ,KINETIC energy ,WAVE energy ,ELECTRON gas - Abstract
We study the linear energy response of the uniform electron gas to an external harmonic perturbation with a focus on resolving different contributions to the total energy. This has been achieved by carrying out highly accurate ab initio path integral Monte Carlo (PIMC) calculations for a variety of densities and temperatures. We report a number of physical insights into effects such as screening and the relative importance of kinetic and potential energies for different wave numbers. A particularly interesting finding is obtained from the observed non-monotonic behavior of the induced change in the interaction energy, which becomes negative for intermediate wave numbers. This effect is strongly dependent on the coupling strength and constitutes further direct evidence for the spatial alignment of electrons introduced in earlier works [T. Dornheim et al., Commun. Phys. 5, 304 (2022)]. The observed quadratic dependence on the perturbation amplitude in the limit of weak perturbations and the quartic dependence of perturbation amplitude corrections are consistent with linear and nonlinear versions of the density stiffness theorem. All PIMC simulation results are freely available online and can be used to benchmark new methods or as input for other calculations. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
25. Breakdown of dipole Born approximation and the role of Rydberg's predissociation for the electron-induced ion-pair dissociation to oxygen in the presence of background gases.
- Author
-
Kundu, Narayan, Kumar, Vikrant, and Nandi, Dhananjay
- Subjects
ANGULAR distribution (Nuclear physics) ,KINETIC energy ,COLLISION induced dissociation ,RYDBERG states ,QUANTUM coherence ,MOMENTUM transfer - Abstract
We study the electron-induced ion-pair dissociation to gas-phase oxygen molecules using a state-of-the-art velocity-map ion-imaging technique. The analysis is entirely based on the conical time-gated wedge-shaped velocity slice images of O
− /O2 nascent anionic fragments, and the resulting observations are in favor of Van Brunt et al.'s report [R. J. Van Brunt and L. J. Kieffer, J. Chem. Phys. 60, 3057 (1974)]. A new image reconstruction method, Jacobian over parallel slicing, is introduced to overcome the drawback of ion exaggeration in determining the kinetic energy distribution from the time-gated parallel slicing technique, which offers an alternative approach to the wedge slicing method. Most importantly, the role of the quintet-heavy Rydberg state has been drawn out to the complex ion-pair formalism. The extracted kinetic energy and angular distributions from the wedge slice images reveal a high momentum transfer during the ion-pair dissociation process, which could be the finest rationale to observe the breakdown of dipole Born approximation driven by multipole moment associated with the incident electron beam. Three distinct dissociative momentum bands have been precisely identified for O− dissociation. However, radiationless Rydberg's predissociation continuum (≥15%) has become an inherent character of electron-induced ion-pair dissociation, which could be dealt with using the beyond Born–Oppenheimer treatment. The incoherent sum of Σ and Π symmetric-associated ion-pair final states has been precisely identified by modeling the angular distribution of O− /O2 for each of the kinetic energy bands. A negligibly small amount of forward–backward asymmetry is observed in the angular distribution of O− /O2 , which might be explained by the dissociative state-specific quantum coherence mechanism as reported [Krishnakumar et al., Nat. Phys. 14, 149 (2018); Kumar et al., arXiv:2206.15024 (2022)] by Prabhudesai et al. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
26. Communication: Favorable dimensionality scaling of rectangular collocation with adaptable basis functions up to 7 dimensions.
- Author
-
Manzhos, Sergei, Chan, Matthew, and Carrington, Tucker
- Subjects
COLLOCATION methods ,AB initio quantum chemistry methods ,SCHRODINGER equation ,ACETIC acid ,TITANIUM dioxide ,SCALING laws (Statistical physics) ,WAVE functions ,KINETIC energy - Abstract
We show that by using a rectangular collocation method with a small basis of parameterized functions, it is possible to compute a vibrational spectrum by solving the Schrödinger equation in 7D from a small number of ab initio calculations without a potential surface. The method is ideal for spectra of molecules adsorbed on a surface. In this paper, it is applied to calculate experimentally relevant energy levels of acetic acid adsorbed on the (101) surface of anatase TiO2. In this case, to obtain levels of experimental accuracy, increasing the number of dimensions from 4 to 7 increases the number of required potential points from about 1000 to about 10 000 and the number of basis functions from 126 to 792: the scaling is very attractive. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
27. Role of the Cohen–Fano interference in recoil-induced rotation.
- Author
-
Liu, Ji-Cai, Wang, Jian, Ignatova, Nina, Krasnov, Pavel, Gel'mukhanov, Faris, and Kimberg, Victor
- Subjects
WAVE packets ,MOLECULAR orbitals ,KINETIC energy ,SHEAR waves ,DIATOMIC molecules - Abstract
We study the rotational dynamics induced by the recoil effect in diatomic molecules using time-resolved two-color x-ray pump-probe spectroscopy. A short pump x-ray pulse ionizes a valence electron inducing the molecular rotational wave packet, whereas the second time-delayed x-ray pulse probes the dynamics. An accurate theoretical description is used for analytical discussions and numerical simulations. Our main attention is paid to the following two interference effects that influence the recoil-induced dynamics: (i) Cohen–Fano (CF) two-center interference between partial ionization channels in diatomics and (ii) interference between the recoil-excited rotational levels manifesting as the rotational revival structures in the time-dependent absorption of the probe pulse. The time-dependent x-ray absorption is computed for the heteronuclear CO and homonuclear N
2 molecules as showcases. It is found that the effect of CF interference is comparable with the contribution from independent partial ionization channels, especially for the low photoelectron kinetic energy case. The amplitude of the recoil-induced revival structures for the individual ionization decreases monotonously with a decrease in the photoelectron energy, whereas the amplitude of the CF contribution remains sufficient even at the photoelectron kinetic energy below 1 eV. The profile and intensity of the CF interference depend on the phase difference between the individual ionization channels related to the parity of the molecular orbital emitting the photoelectron. This phenomenon provides a sensitive tool for the symmetry analysis of molecular orbitals. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
28. Exploring three-body fragmentation of acetylene trication.
- Author
-
Yadav, Jatin, Safvan, C. P., Bhatt, Pragya, Kumari, Pooja, Singh, Jasmeet, and Rajput, Jyoti
- Subjects
AB-initio calculations ,POTENTIAL energy surfaces ,METASTABLE states ,ACETYLENE ,KINETIC energy - Abstract
The three-body breakup of [ C 2 H 2 ] 3 + formed in collision with Xe
9+ moving at 0.5 atomic units of velocity is studied by using recoil ion momentum spectroscopy. Three-body breakup channels leading to (H+ , C+ , CH+ ) and (H+ , H+ , C 2 + ) fragments are observed in the experiment and their kinetic energy release is measured. The breakup into (H+ , C+ , CH+ ) occurs via concerted and sequential modes, whereas the breakup into (H+ , H+ , C 2 + ) shows only the concerted mode. By collecting events coming exclusively from the sequential breakup leading to (H+ , C+ , CH+ ), we have determined the kinetic energy release for the unimolecular fragmentation of the molecular intermediate, [ C 2 H ] 2 + . By using ab initio calculations, the potential energy surface for the lowest electronic state of [ C 2 H ] 2 + is generated, which shows the existence of a metastable state with two possible dissociation pathways. A discussion on the agreement between our experimental results and these ab initio calculations is presented. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
29. Multiplicative potentials for kinetic energy and exact exchange.
- Author
-
Oueis, Yan and Staroverov, Viktor N.
- Subjects
KINETIC energy ,POTENTIAL energy ,INTEGRAL operators ,DIFFERENTIAL operators ,QUANTUM chemistry ,DENSITY matrices ,ELECTRON density - Abstract
Harriman showed that within finite basis sets of one-electron functions that form linearly independent products (LIP), differential and integral operators can be represented exactly and unambiguously by multiplicative (local) potentials. Although almost no standard basis sets of quantum chemistry form LIPs in a numerical sense, occupied self-consistent field (SCF) orbitals routinely do so. Using minimal LIP basis sets of occupied SCF orbitals, we construct multiplicative potentials for electronic kinetic energy and exact exchange that reproduce the Hartree–Fock and Kohn–Sham Hamiltonian matrices and electron densities for atoms and molecules. The results highlight fundamental differences between local and nonlocal operators and suggest a practical possibility of developing exact kinetic energy functionals within finite basis sets by using effective local potentials. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
30. Exact constraints and appropriate norms in machine-learned exchange-correlation functionals.
- Author
-
Pokharel, Kanun, Furness, James W., Yao, Yi, Blum, Volker, Irons, Tom J. P., Teale, Andrew M., and Sun, Jianwei
- Subjects
FUNCTIONALS ,ELECTRON density ,KINETIC energy ,MACHINE learning ,ENERGY density - Abstract
Machine learning techniques have received growing attention as an alternative strategy for developing general-purpose density functional approximations, augmenting the historically successful approach of human-designed functionals derived to obey mathematical constraints known for the exact exchange-correlation functional. More recently, efforts have been made to reconcile the two techniques, integrating machine learning and exact-constraint satisfaction. We continue this integrated approach, designing a deep neural network that exploits the exact constraint and appropriate norm philosophy to de-orbitalize the strongly constrained and appropriately normed (SCAN) functional. The deep neural network is trained to replicate the SCAN functional from only electron density and local derivative information, avoiding the use of the orbital-dependent kinetic energy density. The performance and transferability of the machine-learned functional are demonstrated for molecular and periodic systems. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
31. Can the Hartree–Fock kinetic energy exceed the exact kinetic energy?
- Author
-
Crisostomo, S., Levy, M., and Burke, K.
- Subjects
KINETIC energy ,VIRIAL theorem ,CHEMICAL bond lengths ,INTUITION - Abstract
The Hartree–Fock (HF) approximation has been an important tool for quantum-chemical calculations since its earliest appearance in the late 1920s and remains the starting point of most single-reference methods in use today. Intuition suggests that the HF kinetic energy should not exceed the exact kinetic energy; but no proof of this conjecture exists, despite a near century of development. Beginning from a generalized virial theorem derived from scaling considerations, we derive a general expression for the kinetic energy difference that applies to all systems. For any atom or ion, this trivially reduces to the well-known result that the total energy is the negative of the kinetic energy and, since correlation energies are never positive, proves the conjecture in this case. Similar considerations apply to molecules at their equilibrium bond lengths. We use highly precise calculations on Hooke's atom (two electrons in a parabolic well) to test the conjecture in a nontrivial case and to parameterize the difference between density functional and HF quantities, but find no violations of the conjecture. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
32. Spin and alignment effects in O2 chemisorption on Fe(110), Ni(111), and Co(0001) films grown on W(110).
- Author
-
Kurahashi, Mitsunori
- Subjects
CHEMISORPTION ,ELECTRON spin ,KINETIC energy - Abstract
O
2 has a spin triplet multiplicity in its ground state, while the effect of its electron spin on O2 -surface interaction is not well understood. In this study, the spin and/or alignment effects in O2 chemisorption on surfaces of Fe(110), Ni(111), and Co(0001) films grown on W(110) have been investigated with the use of a single spin-rotational state-selected O2 beam. The results indicate that the spin effects for the Fe and Ni films are similar in that the initial sticking probability (S0 ) of O2 is higher when the spins of O2 and the film are antiparallel, and the spin dependence in S0 , which amounts to 30%–40% at thermal energy, decays with increasing the O2 kinetic energy (E0 ). In the case of the Fe/O2 system, however, considerable spin dependence was found to remain even at E0 > 0.2 eV and on the oxidized surface. It has also been shown that the barrier for O2 chemisorption increases in the order of Fe(110) < Ni(111) < Co(0001), and the difference in the observed alignment effect among the samples can be understood based on the difference in the barrier. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
33. Comparing correlation components and approximations in Hartree–Fock and Kohn–Sham theories via an analytical test case study.
- Author
-
Giarrusso, Sara and Pribram-Jones, Aurora
- Subjects
HARTREE-Fock approximation ,HUBBARD model ,FUNCTIONALS ,KINETIC energy ,DIMERS - Abstract
The asymmetric Hubbard dimer is a model that allows for explicit expressions of the Hartree–Fock (HF) and Kohn–Sham (KS) states as analytical functions of the external potential, Δv, and of the interaction strength, U. We use this unique circumstance to establish a rigorous comparison between the individual contributions to the correlation energies stemming from the two theories in the {U, Δv} parameter space. Within this analysis of the Hubbard dimer, we observe a change in the sign of the HF kinetic correlation energy, compare the indirect repulsion energies, and derive an expression for the "traditional" correlation energy, i.e., the one that corrects the HF estimate, in a pure site-occupation function theory spirit [Eq. (45)]. Next, we test the performances of the Liu–Burke and the Seidl–Perdew–Levy functionals, which model the correlation energy based on its weak- and strong-interaction limit expansions and can be used for both the traditional and the KS correlation energies. Our results show that, in the Hubbard dimer setting, they typically work better for the HF reference, despite having been originally devised for KS. These conclusions are somewhat in line with prior assessments of these functionals on various chemical datasets. However, the Hubbard dimer model allows us to show the extent of the error that may occur in using the strong-interaction ingredient for the KS reference in place of the one for the HF reference, as has been carried out in most of the prior assessments. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
34. Solid-state performance of a meta-GGA screened hybrid density functional constructed from Pauli kinetic enhancement factor dependent semilocal exchange hole.
- Author
-
Jana, Subrata, Constantin, Lucian A., Śmiga, Szymon, and Samal, Prasanjit
- Subjects
DENSITY functionals ,REVERSE engineering ,TAYLOR'S series ,MATERIALS science ,KINETIC energy - Abstract
The semilocal form of an exchange hole is highly useful in developing non-local range-separated hybrid density functionals for finite and extended systems. The way to construct the conventional exact exchange hole model is based on either the Taylor series expansion or the reverse engineering technique from the corresponding exchange energy functional. Although the latter technique is quite popular in the context of generalized gradient approximation (GGA) functionals, the same for the meta-GGA functionals is not so much explored. Thus, in this study, we propose a reverse-engineered semilocal exchange hole of a meta-GGA functional, which only depends on the meta-GGA ingredient α (also known as the Pauli kinetic energy enhancement factor). The model is subsequently used to design the short-range-separated meta-GGA hybrid density functional. We show that the present method can be successfully applied for several challenging problems in the context of solids, especially for which the GGA based hybrid fails drastically. This assessment proves that the present functional is quite useful for materials sciences. Finally, we also use this method for several molecular test cases, where the results are also as comparative as its base semilocal functional. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
35. Successes and challenges in using machine-learned activation energies in kinetic simulations.
- Author
-
Ismail, I., Robertson, C., and Habershon, S.
- Subjects
CHEMICAL properties ,ARTIFICIAL neural networks ,AB-initio calculations ,KINETIC energy ,CHEMICAL reactions ,ACTIVATION energy - Abstract
The prediction of the thermodynamic and kinetic properties of chemical reactions is increasingly being addressed by machine-learning (ML) methods, such as artificial neural networks (ANNs). While a number of recent studies have reported success in predicting chemical reaction activation energies, less attention has been focused on how the accuracy of ML predictions filters through to predictions of macroscopic observables. Here, we consider the impact of the uncertainty associated with ML prediction of activation energies on observable properties of chemical reaction networks, as given by microkinetics simulations based on ML-predicted reaction rates. After training an ANN to predict activation energies, given standard molecular descriptors for reactants and products alone, we performed microkinetics simulations of three different prototypical reaction networks: formamide decomposition, aldol reactions, and decomposition of 3-hydroperoxypropanal. We find that the kinetic modeling predictions can be in excellent agreement with corresponding simulations performed with ab initio calculations, but this is dependent on the inherent energetic landscape of the networks. We use these simulations to suggest some guidelines for when ML-based activation energies can be reliable and when one should take more care in applications to kinetics modeling. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
36. Thermochemistry and mechanisms of the Pt+ + SO2 reaction from guided ion beam tandem mass spectrometry and theory.
- Author
-
Armentrout, P. B.
- Subjects
THERMOCHEMISTRY ,ENDOTHERMIC reactions ,KINETIC energy ,MASS spectrometers ,ION beams ,POTENTIAL energy - Abstract
The kinetic energy dependences of the reactions of Pt
+ (2 D5/2 ) with SO2 were studied using a guided ion beam tandem mass spectrometer and theory. The observed cationic products are PtO+ and PtSO+ , with small amounts of PtS+ , all formed in endothermic reactions. Modeling the kinetic energy dependent product cross sections allows determination of the product bond dissociation energies (BDEs): D0 (Pt+ –O) = 3.14 ± 0.11 eV, D0 (Pt+ –S) = 3.68 ± 0.31 eV, and D0 (Pt+ –SO) = 3.03 ± 0.12 eV. The oxide BDE agrees well with more precise literature values, whereas the latter two results are the first such measurements. Quantum mechanical calculations were performed for PtO+ , PtS+ , PtO2 + , and PtSO+ at the B3LYP and coupled-cluster with single, double, and perturbative triple [CCSD(T)] levels of theory using the def2-XZVPPD (X = T, Q) and aug-cc-pVXZ (X = T, Q, 5) basis sets and complete basis set extrapolations. These theoretical BDEs agree well with the experimental values. After including empirical spin–orbit corrections, the product ground states are determined as PtO+ (4 Σ3/2 ), PtS+ (4 Σ3/2 ), PtO2 + (2 Σg + ), and PtSO+ (2 A′). Potential energy profiles including intermediates and transition states for each reaction were also calculated at the B3LYP/def2-TZVPPD level. Periodic trends in the thermochemistry of the group 9 metal chalcogenide cations are compared, and the formation of PtO+ from the Pt+ + SO2 reaction is compared with those from the Pt+ + O2 , CO2 , CO, and NO reactions. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
37. A neural network-assisted open boundary molecular dynamics simulation method.
- Author
-
Floyd, J. E. and Lukes, J. R.
- Subjects
NEURAL circuitry ,CANONICAL ensemble ,KINETIC energy ,POTENTIAL energy ,MOLECULAR dynamics ,ATOMIC models ,SYSTEM dynamics - Abstract
A neural network-assisted molecular dynamics method is developed to reduce the computational cost of open boundary simulations. Particle influxes and neural network-derived forces are applied at the boundaries of an open domain consisting of explicitly modeled Lennard-Jones atoms in order to represent the effects of the unmodeled surrounding fluid. Canonical ensemble simulations with periodic boundaries are used to train the neural network and to sample boundary fluxes. The method, as implemented in the LAMMPS, yields temperature, kinetic energy, potential energy, and pressure values within 2.5% of those calculated using periodic molecular dynamics and runs two orders of magnitude faster than a comparable grand canonical molecular dynamics system. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
38. Reduced-dimensional vibrational models of the water dimer.
- Author
-
Vogt, Emil, Simkó, Irén, Császár, Attila G., and Kjaergaard, Henrik G.
- Subjects
POTENTIAL energy surfaces ,WATER levels ,KINETIC energy - Abstract
A model based on the finite-basis representation of a vibrational Hamiltonian expressed in internal coordinates is developed. The model relies on a many-mode, low-order expansion of both the kinetic energy operator and the potential energy surface (PES). Polyad truncations and energy ceilings are used to control the size of the vibrational basis to facilitate accurate computations of the OH stretch and HOH bend intramolecular transitions of the water dimer ( H 2 16 O)
2 . Advantages and potential pitfalls of the applied approximations are highlighted. The importance of choices related to the treatment of the kinetic energy operator in reduced-dimensional calculations and the accuracy of different water dimer PESs are discussed. A range of different reduced-dimensional computations are performed to investigate the wavenumber shifts in the intramolecular transitions caused by the coupling between the intra- and intermolecular modes. With the use of symmetry, full 12-dimensional vibrational energy levels of the water dimer are calculated, predicting accurately the experimentally observed intramolecular fundamentals. It is found that one can also predict accurate intramolecular transition wavenumbers for the water dimer by combining a set of computationally inexpensive reduced-dimensional calculations, thereby guiding future effective-Hamiltonian treatments. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
39. Generalized elimination of the global translation from explicitly correlated Gaussian functions.
- Author
-
Muolo, Andrea, Mátyus, Edit, and Reiher, Markus
- Subjects
GAUSSIAN function ,PARTICLES ,KINETIC energy ,SCHRODINGER equation ,GENERALIZATION - Abstract
This paper presents the multi-channel generalization of the center-of-mass kinetic energy elimination approach [B. Simmen
et al. , Mol. Phys.111 , 2086 (2013)] when the Schrödinger equation is solved variationally with explicitly correlated Gaussian functions. The approach has immediate relevance in many-particle systems which are handled without the Born–Oppenheimer approximation and can be employed also for Dirac-type Hamiltonians. The practical realization and numerical properties of solving the Schrödinger equation in laboratory-frame Cartesian coordinates are demonstrated for the ground rovibronic state of the H 2 + = { p + , p + , e − } ion and the H2 = {p+ , p+ , e− , e− } molecule. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
40. Assessing models of force-dependent unbinding rates via infrequent metadynamics.
- Author
-
Peña Ccoa, Willmor J. and Hocky, Glen M.
- Subjects
PROTEIN-ligand interactions ,CELL physiology ,EIGENFUNCTIONS ,KINETIC energy ,SAMPLING (Process) - Abstract
Protein–ligand interactions are crucial for a wide range of physiological processes. Many cellular functions result in these non-covalent "bonds" being mechanically strained, and this can be integral to proper cellular function. Broadly, two classes of force dependence have been observed—slip bonds, where the unbinding rate increases, and catch bonds, where the unbinding rate decreases. Despite much theoretical work, we cannot predict for which protein–ligand pairs, pulling coordinates, and forces a particular rate dependence will appear. Here, we assess the ability of MD simulations combined with enhanced sampling techniques to probe the force dependence of unbinding rates. We show that the infrequent metadynamics technique correctly produces both catch and slip bonding kinetics for model potentials. We then apply it to the well-studied case of a buckyball in a hydrophobic cavity, which appears to exhibit an ideal slip bond. Finally, we compute the force-dependent unbinding rate of biotin–streptavidin. Here, the complex nature of the unbinding process causes the infrequent metadynamics method to begin to break down due to the presence of unbinding intermediates, despite the use of a previously optimized sampling coordinate. Allowing for this limitation, a combination of kinetic and free energy computations predicts an overall slip bond for larger forces consistent with prior experimental results although there are substantial deviations at small forces that require further investigation. This work demonstrates the promise of predicting force-dependent unbinding rates using enhanced sampling MD techniques while also revealing the methodological barriers that must be overcome to tackle more complex targets in the future. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
41. The dynamics of CO production from the photolysis of acetone across the whole S1 ← S0 absorption spectrum: Roaming and triple fragmentation pathways.
- Author
-
Jacob, L. S. D., Lee, K. L. K., Schmidt, T. W., Nauta, K., and Kable, S. H.
- Subjects
ABSORPTION spectra ,EXCITED states ,KINETIC energy ,PHOTODISSOCIATION ,PHOTOCHEMISTRY ,SCISSION (Chemistry) ,ACETONE - Abstract
The unimolecular photodissociation dynamics of acetone spanning the entire S
1 ← S0 absorption spectrum have been reinvestigated, with a focus on mechanisms that produce CO. At excitation wavelengths of λ > 305.8 nm, all photoproducts are formed on the S0 state after internal conversion. A roaming mechanism forming C2 H6 + CO is active in the window λ = 311.2–305.8 nm. From λ = 305.8 to 262 nm, little or no CO is produced with the photochemistry dominated by the Norrish-type I C–C bond cleavage on the lowest excited triplet state, T1 . At higher energy (λ < 262 nm), an increasing fraction of CH3 CO radicals from the primary reaction have sufficient internal energy to spontaneously decompose to CH3 + CO. A new model is presented to account for the kinetic energy distribution of the secondary CH3 radical, allowing us to determine the height of the energetic barrier to CH3 CO decomposition as 68 ± 4 kJ mol−1 , which lies midway between previous measurements. The fraction of CO from triple fragmentation rises smoothly from 260 to 248 nm. We see no evidence of the return of roaming, or any other S0 reaction, in this higher energy region of the first electronic absorption band. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
42. Mechanism for the rare fluctuation that powers protein conformational change.
- Author
-
Wu, Shanshan and Ma, Ao
- Subjects
ACTIVATION energy ,KINETIC energy ,ENERGY transfer ,PROTEINS ,ISOMERIZATION - Abstract
Most functional processes of biomolecules are rare events. Key to a rare event is the rare fluctuation that enables the energy activation process that precedes and powers crossing of the activation barrier. However, the physical nature of this rare fluctuation and how it enables energy activation and subsequently barrier crossing are unknown. We developed a novel metric, the reaction capacity p
C , that rigorously defines the beginning and parameterizes the progress of energy activation. This enabled us to identify the rare fluctuation as a special phase-space condition that is necessary and sufficient for initiating systematic energy flow from the non-reaction coordinates into the reaction coordinates. The energy activation of a prototype biomolecular isomerization reaction is dominated by kinetic energy transferring into and accumulating in the reaction coordinates, administered by inertial forces alone. This mechanism for energy activation is fundamentally different from the mechanism suggested by Kramers theory. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
43. Unexplained dissociation pathways of two-body fragmentation of methane dication.
- Author
-
Rajput, Jyoti, Garg, Diksha, Cassimi, A., Méry, A., Fléchard, X., Rangama, J., Guillous, S., Iskandar, W., Agnihotri, A. N., Matsumoto, J., Ahuja, R., and Safvan, C. P.
- Subjects
AB-initio calculations ,ION-molecule collisions ,ELECTRON configuration ,BRANCHING ratios ,KINETIC energy - Abstract
The ion-induced fragmentation of C H 4 2 + into H
+ and C H 3 + is studied using a cold target recoil ion momentum spectroscopy in coincidence with the charge state of the post-collision projectile. Using constant velocity Ar9+ and N3+ , results from four different datasets are presented, with a selection on the final charge state of the projectile (Ar8+ or Ar7+ and N2+ or N+ ). Three distinct dissociation pathways (I, II, and III) are observed for each dataset, with the mean kinetic energy release values of around 4.7, 5.8, and 7.9 eV, respectively. The electronic states that are populated correspond to electronic configurations (1 t 2 ) − 2 and (2 a 1 ) − 1 (1 t 2 ) − 1 of the methane dication, C H 4 2 + . The relative branching ratios between the three pathways are discussed as a function of the charge state of the post-collision projectile, and a strong correlation with the specific nature of the ion–molecule interaction is found. The existing ab initio calculations have provided an explanation only for pathway II. In this article, we propose an explanation for pathway III, but pathway I still remains unexplained and requires further theoretical efforts. A discussion of the dependence of dissociation on the mode of excitation is presented. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
44. Accurate parameterization of the kinetic energy functional.
- Author
-
Kumar, Shashikant, Borda, Edgar Landinez, Sadigh, Babak, Zhu, Siya, Hamel, Sebastian, Gallagher, Brian, Bulatov, Vasily, Klepeis, John, and Samanta, Amit
- Subjects
KINETIC energy ,DENSITY functional theory ,ENERGY density ,DENSITY functionals ,PARAMETERIZATION - Abstract
The absence of a reliable formulation of the kinetic energy density functional has hindered the development of orbital free density functional theory. Using the data-aided learning paradigm, we propose a simple prescription to accurately model the kinetic energy density of any system. Our method relies on a dictionary of functional forms for local and nonlocal contributions, which have been proposed in the literature, and the appropriate coefficients are calculated via a linear regression framework. To model the nonlocal contributions, we explore two new nonlocal functionals—a functional that captures fluctuations in electronic density and a functional that incorporates gradient information. Since the analytical functional forms of the kernels present in these nonlocal terms are not known from theory, we propose a basis function expansion to model these seemingly difficult nonlocal quantities. This allows us to easily reconstruct kernels for any system using only a few structures. The proposed method is able to learn kinetic energy densities and total kinetic energies of molecular and periodic systems, such as H
2 , LiH, LiF, and a one-dimensional chain of eight hydrogens using data from Kohn–Sham density functional theory calculations for only a few structures. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
45. Self-assembling of the neutral intermediate with chemically bound argon in photoexcited van der Waals complex Ar–I2.
- Author
-
Bogomolov, Alexandr S., Dozmorov, Nikolay V., Kochubei, Sergei A., and Baklanov, Alexey V.
- Subjects
VAN der Waals clusters ,ARGON ,NOBLE gases ,KINETIC energy ,CHARGE exchange - Abstract
Photodissociation of the van der Waals complex Ar–I
2 after excitation into the Rydberg states of I2 has been investigated with velocity map imaging of photofragments. Formation of the translationally hot ions of argon Ar+ with three modes in kinetic energy distribution has been revealed. The measured dependence of the kinetic energy of Ar+ on the pumping photon energy indicates the appearance of Ar+ from three channels of the photodissociation of the linear intermediate Ar+ –I–I− containing chemically bound argon. These channels are (1) dissociation into Ar+ + I2 − ; (2) three-body dissociation into (Ar+ )* + I* + I− , with (Ar+ )* and I* being the2 P1/2 states of the species; and (3) two-body electron photodetachment, giving rise to Ar+ + I2 + e. Three indicated channels are similar to those established for the photodissociation of trihalide anions. This similarity confirms the conclusion on the formation of the Ar+ –I–I− intermediate, which is isoelectronic to the trihalide anion Cl–I–I− . The mechanism of the Ar+ –I–I− formation involves two-photon excitation of the complex Ar–I2 into the Rydberg state of I2 converted into the ion-pair state and further electron transfer from Ar to I+ of the ion-pair state. The self-assembling of the structure making the formation of the Ar+ –I–I− intermediate energetically accessible is confirmed by modeling the dynamics in the excited linear complex Ar–I2 . Photoexcitation of the van der Waals complexes of noble gases with halogens into the ion-pair states of halogen is supposed to be a promising approach for generating the new chemical compounds of noble gas atoms. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
46. Quantum nature of molecular vibrational quenching: Water–molecular hydrogen collisions.
- Author
-
Wiesenfeld, Laurent
- Subjects
KINETIC energy ,QUANTUM computing ,MOLECULAR collisions ,QUANTUM numbers ,ENERGY transfer - Abstract
Rates of conversions of molecular internal energy to and from kinetic energy by means of molecular collision allow us to compute collisional line shapes and transport properties of gases. Knowledge of ro-vibrational quenching rates is necessary to connect spectral observations to physical properties of warm astrophysical gasses, including exo-atmospheres. For a system of paramount importance in this context, the vibrational bending mode quenching of H
2 O by H2 , we show here that the exchange of vibrational to rotational and kinetic energy remains a quantum process, despite the large numbers of quantum levels involved and the large vibrational energy transfer. The excitation of the quantized rotor of the projectile is by far the most effective ro-vibrational quenching path of water. To do so, we use a fully quantum first-principles computation, potential and dynamics, converging it at all stages, in a full coupled channel formalism. We present here rates for the quenching of the first bending mode of ortho-H2 O by ortho-H2 , up to 500 K, in a fully converged coupled channel formalism. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
47. Using nondirect product Wigner D basis functions and the symmetry-adapted Lanczos algorithm to compute the ro-vibrational spectrum of CH4–H2O.
- Author
-
Wang, Xiao-Gang and Carrington, Tucker
- Subjects
LANCZOS method ,VAN der Waals forces ,KINETIC energy - Abstract
By doing calculations on the methane–water van der Waals complex, we demonstrate that highly converged energy levels and wavefunctions can be obtained using Wigner D basis functions and the Symmetry-Adapted Lanczos (SAL) method. The Wigner D basis is a nondirect product basis and, therefore, efficient when the kinetic energy operator has accessible singularities. The SAL method makes it possible to exploit symmetry to label energy levels and reduce the cost of the calculation, without explicitly using symmetry-adapted basis functions. Line strengths are computed, and new bands are identified. In particular, we find unusually strong transitions between states associated with the isomers of the global minimum and the secondary minimum. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
48. Direct product-type grid representations for angular coordinates in extended space and their application in the MCTDH approach.
- Author
-
Zhao, Bin and Manthe, Uwe
- Subjects
CENTRAL processing units ,POTENTIAL energy surfaces ,QUANTUM theory ,KINETIC energy ,COORDINATES ,MAGNITUDE (Mathematics) ,EQUATIONS of motion - Abstract
Multi-configurational time-dependent Hartree (MCTDH) calculations using time-dependent grid representations can be used to accurately simulate high-dimensional quantum dynamics on general ab initio potential energy surfaces. Employing the correlation discrete variable representation, sets of direct product type grids are employed in the calculation of the required potential energy matrix elements. This direct product structure can be a problem if the coordinate system includes polar and azimuthal angles that result in singularities in the kinetic energy operator. In the present work, a new direct product-type discrete variable representation (DVR) for arbitrary sets of polar and azimuthal angles is introduced. It employs an extended coordinate space where the range of the polar angles is taken to be [−π, π]. The resulting extended space DVR resolves problems caused by the singularities in the kinetic energy operator without generating a very large spectral width. MCTDH calculations studying the F·CH
4 complex are used to investigate important properties of the new scheme. The scheme is found to allow for more efficient integration of the equations of motion compared to the previously employed cot-DVR approach [G. Schiffel and U. Manthe, Chem. Phys. 374, 118 (2010)] and decreases the required central processing unit times by about an order of magnitude. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
49. Simulation of the effect of vibrational pre-excitation on the dynamics of pyrrole photo-dissociation.
- Author
-
Makhov, Dmitry V. and Shalashilin, Dmitrii V.
- Subjects
PYRROLES ,ULTRAVIOLET lasers ,LASER pulses ,KINETIC energy - Abstract
Photo-dissociation dynamics is simulated for vibrationally pre-excited pyrrole molecules using an ab initio multiple cloning approach. Total kinetic energy release (TKER) spectra and dissociation times are calculated. It is found that pre-excitation of N–H bond vibrations facilitates fast direct dissociation, which results in a significant increase in the high-energy wing of TKER spectra. The results are in very good agreement with the recent vibrationally mediated photo-dissociation experiment, where the TKER spectrum was measured for pyrrole molecules excited by a combination of IR and UV laser pulses. Calculations for other vibrational modes show that this effect is specific for N–H bond vibrations: Pre-excitation of other modes does not result in any significant changes in TKER spectra. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
50. Kinetic energy deposited into a nanodroplet, cluster, or molecule in a sticking collision with background gas.
- Author
-
Liang, Jiahao and Kresin, Vitaly V.
- Subjects
KINETIC energy ,GASES ,MOLECULES - Abstract
In processes when particles such as nanodroplets, clusters, or molecules move through a dilute background gas and undergo capture collisions, it is often important to know how much translational kinetic energy is deposited into the particles by these pick-up events. For sticking collisions with a Maxwell–Boltzmann gas, an exact expression is derived, which is valid for arbitrary relative magnitudes of the particle and thermal gas speeds. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.