A walk through the approximations of <i>ab initio</i> multiple spawning

Mignolet, Benoît; Curchod, Basile F. E.

doi:10.1063/1.5022877

Cited by 63 publications

(70 citation statements)

References 98 publications

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“…Higher order saddle point approximations are also possible, by also calculating first and/or second derivatives of the electronic energies and/or nonadiabatic coupling matrix elements. 142 However, this has rarely been pursued because of the considerable expense AIMS Review -Page 28 associated with derivatives of the nonadiabatic coupling matrix elements or second derivatives of the electronic energy. A promising alternative that has been recently suggested uses Gaussian process regression to calculate these matrix elements.…”

Section: Ab Initio Multiple Spawningmentioning

confidence: 99%

Ab Initio Nonadiabatic Quantum Molecular Dynamics

2018

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The Born-Oppenheimer approximation underlies much of chemical simulation and provides the framework defining the potential energy surfaces that are used for much of our pictorial understanding of chemical phenomena. However, this approximation breaks down when the dynamics of molecules in excited electronic states are considered. Describing dynamics when the Born-Oppenheimer approximation breaks down requires a quantum mechanical description of the nuclei. Chemical reaction dynamics on excited electronic states is critical for many applications in renewable energy, chemical synthesis, and bioimaging. Furthermore, it is necessary in order to connect with many ultrafast pump-probe spectroscopic experiments. In this review, we provide an overview of methods that can describe nonadiabatic dynamics, with emphasis on those that are able to simultaneously address the quantum mechanics of both electrons and nuclei. Such ab initio quantum molecular dynamics methods solve the electronic Schrödinger equation alongside the nuclear dynamics and thereby avoid the need for precalculation of potential energy surfaces and nonadiabatic coupling matrix elements. Two main families of methods are commonly employed to simulate nonadiabatic dynamics in molecules: full quantum dynamics, such as the multiconfigurational time-dependent Hartree method, and classical trajectory-based approaches, such as trajectory surface hopping. In this review, we describe a third class of methods that is intermediate between the two: Gaussian basis set expansions built around trajectories.

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Section: Ab Initio Multiple Spawningmentioning

confidence: 99%

Ab Initio Nonadiabatic Quantum Molecular Dynamics

2018

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“…In this sense, FMS is in principle exact when a large number of TBFs is employed, as discussed in Ref. 54. FMS is in principle exact, but the numerically-exact calculation of the integrals necessary to couple the TBFs requires to know the potential energy surfaces and nonadiabatic coupling terms over the entire molecular configuration space, 54 making the method intractable for molecular systems. Two approximations can be deployed to simplify these integrals: (i ) the saddle-point approximation (SPA), where the nuclear-coordinate dependence of the electronic structure quantity in the integrand is approximated by a truncated Taylor expansion at the centroid position of the two TBFs, and (ii ) the independent first generation approximation (IFGA), where the initial (parent) TBFs describing the nuclear wavefunction (or wavepacket) at time t = 0 are considered uncoupled.…”

Section: Full-and Ab Initio Multiple Spawningmentioning

confidence: 99%

“…53 In a previous work, we proposed a detailed test of the different approximations linking the in-principle exact XFFMS to XFAIMS for photoexcitation processes. 54 Here, we aim at validating the use of XFAIMS for the description of molecular photoexcitation by comparing it to TSH and numerically-exact quantum dynamics (QD) simulations. We show that XFAIMS, thanks to its use of coupled traveling basis functions, reproduces at least qualitatively the QD results for processes involving long or multiple pulses, which otherwise leads to a breakdown of the TSH approximations.…”

Section: Introductionmentioning

confidence: 99%

Excited-State Molecular Dynamics Triggered by Light Pulses—Ab Initio Multiple Spawning vs Trajectory Surface Hopping

Mignolet

Curchod

2019

J. Phys. Chem. A

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Trajectory surface hopping and ab initio multiple spawning are two commonly employed methods for simulating the excited-state dynamics of molecules. Trajectory surface hopping portrays the dynamics of nuclear wavepackets by a swarm of independent classical trajectories, which can hop between electronic states. Ab initio multiple spawning, on the other hand, expresses nuclear wavepackets in a basis of traveling, coupled basis functions, whose number can be extended in case of coupling between electronic states. In the following, we propose to compare the performance of these two methods to describe processes involving the explicit interaction of a molecule with laser pulses. We base this comparison on the LiH molecule, as it is compatible with numerically-exact simulations using quantum dynamics. As recognized in earlier works, the limitations of TSH due to its inherent independent trajectory approximation are further enhanced when studying an explicit photoexcitation. While ab initio multiple spawning is also based on a series of approximations, the couplings between its traveling basis functions allow for a proper description of phenomena that TSH cannot describe with its inherent independent trajectory approximation, even when applying decoherence corrections. We show here for different in silico experiments involving laser pulses that ab initio multiple spawning overcomes the limitations experienced by trajectory surface hopping and offers an at least qualitative description of population transfer between electronic states.

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“…For details and discussions on these two approximations, the reader is referred to Refs. [36,76,73]. AIMS has been coupled with different electronic-structure methods such as SA-CASSCF [77,78], MS-CASPT2 [79], FOMO-CASCI [80], or linear-response TDDFT (LR-TDDFT) [81].…”

Section: Ab Initio Multiple Spawningmentioning

confidence: 99%

CT-MQC – a coupled-trajectory mixed quantum/classical method including nonadiabatic quantum coherence effects

2018

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A walk through the approximations of ab initio multiple spawning

Cited by 63 publications

References 98 publications

Ab Initio Nonadiabatic Quantum Molecular Dynamics

Ab Initio Nonadiabatic Quantum Molecular Dynamics

Excited-State Molecular Dynamics Triggered by Light Pulses—Ab Initio Multiple Spawning vs Trajectory Surface Hopping

CT-MQC – a coupled-trajectory mixed quantum/classical method including nonadiabatic quantum coherence effects

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