A Gaussian wave packet phase-space representation of quantum canonical statistics

Coughtrie, David J.; Tew, David P.

doi:10.1063/1.4927235

Cited by 3 publications

(2 citation statements)

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“…In this particular situation the proposed method is equivalent to methods that have been used before for Gaussian wavefunctions. 94,95 For the frozen Gaussian, the equations of motion, according to the variational principle, arė…”

Section: Theory and Methodsmentioning

confidence: 99%

Classical Wigner model based on a Feynman path integral open polymer

Svensson

Poulsen

Nyman

2020

The Journal of Chemical Physics

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When using mathematical models to computationally investigate a chemical system it is important that the methods used are accurate enough to account for the relevant properties of the system and at the same time simple enough to be computationally affordable. This thesis presents research that so far has resulted in three published papers and one unpublished manuscript. It concerns the application and development of computational methods for chemistry, with some extra emphasis on the calculation of reaction rate constants. In astrochemistry radiative association is a relevant reaction mechanism for the formation of molecules. The rate constants for such reactions are often difficult to obtain though experiments. In the first published paper of the thesis a rate constant for the formation of the hydroxyl radical, through the radiative association of atomic oxygen and hydrogen, is presented. This rate constant was calculated by a combination of different methods and should be an improvement over previously available rate constants. In the the second published paper of this thesis two kinds of basis functions, for use with a variational principle for the dynamics of quantum distributions in phase space, i.e. Wigner functions, is presented. These are tested on model systems and found to have some appealing properties. The classical Wigner method is an approximate method of simulation, where an initial quantum distribution is propagated in time with classical mechanics. In the third published paper of this thesis a new method of sampling the initial quantum distribution, with an imaginary time Feynman path integral, is derived and tested on model systems. In the unpublished manuscript, this new method is applied to reaction rate constants and tested on two model sysv Abstract tems. The new sampling method shows some promise for future applications. vi Preface You have guessed right; I have lately been so deeply engaged in one occupation that I have not allowed myself sufficient rest, as you see: but I hope, I sincerely hope, that all these employments are now at an end, and that I am at length free.

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Section: Theory and Methodsmentioning

confidence: 99%

Classical Wigner model based on a Feynman path integral open polymer

Svensson

Poulsen

Nyman

2020

The Journal of Chemical Physics

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“…12,13 An important area of application is on-the-fly dynamics, e.g., in the Ab Initio Multiple Spawning (AIMS) approach, 14,15 the Direct Dynamics variational Multi-Configurational Gaussian (DD-vMCG) method, [16][17][18] the ab initio Multiple Cloning Multi-Configurational Ehrenfest (AIMC-MCE) approach, 19 and the on-the-fly ab initio (OTF-AI) semiclassical dynamics method. 20 Also, statistical treatments, 21 system-bath problems, 22 and quantum-classical hybrid approaches 11,23 are naturally amenable to a GWP based treatment.…”

Section: Introductionmentioning

confidence: 99%

Multi-layer Gaussian-based multi-configuration time-dependent Hartree (ML-GMCTDH) simulations of ultrafast charge separation in a donor–acceptor complex

Maiolo

Worth

Burghardt

2021

The Journal of Chemical Physics

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We report on first applications of the Multi-Layer Gaussian-based Multi-Configuration Time-Dependent Hartree (ML-GMCTDH) method [Römer et al., J. Chem. Phys. 138, 064106 (2013)], beyond its basic two-layer variant. The ML-GMCTDH scheme provides an embedding of a variationally evolving Gaussian wavepacket basis into a hierarchical tensor representation of the wavefunction. A first principles parametrized model Hamiltonian for ultrafast non-adiabatic dynamics in an oligothiophene-fullerene charge transfer complex is employed, relying on a two-state linear vibronic coupling model which combines a distribution of tuning type modes with an intermolecular coordinate that also modulates the electronic coupling.Efficient ML-GMCTDH simulations are carried out for up to 300 vibrational modes, using an implementation within the QUANTICS program. Excellent agreement with reference ML-MCTDH calculations is obtained.

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