Comparing (stochastic-selection) ab initio multiple spawning with trajectory surface hopping for the photodynamics of cyclopropanone, fulvene, and dithiane.

Lea M Ibele,Yorick Lassmann,Todd J Martínez,Basile F E Curchod

doi:10.1063/5.0045572

Lea M Ibele, Yorick Lassmann + Show 2 more

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https://doi.org/10.1063/5.0045572

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Abstract

Ab Initio Multiple Spawning (AIMS) simulates the excited-state dynamics of molecular systems by representing nuclear wavepackets in a basis of coupled traveling Gaussian functions, called trajectory basis functions (TBFs). New TBFs are spawned when nuclear wavepackets enter regions of strong nonadiabaticity, permitting the description of non-Born-Oppenheimer processes. The spawning algorithm is simultaneously the blessing and the curse of the AIMS method: it allows for an accurate description of the transfer of nuclear amplitude between different electronic states, but it also dramatically increases the computational cost of the AIMS dynamics as all TBFs are coupled. Recently, a strategy coined stochastic-selection AIMS (SSAIMS) was devised to limit the ever-growing number of TBFs and tested on simple molecules. In this work, we use the photodynamics of three different molecules-cyclopropanone, fulvene, and 1,2-dithiane-to investigate (i) the potential of SSAIMS to reproduce reference AIMS results for challenging nonadiabatic dynamics, (ii) the compromise achieved by SSAIMS in obtaining accurate results while using the smallest average number of TBFs as possible, and (iii) the performance of SSAIMS in comparison to the mixed quantum/classical method trajectory surface hopping (TSH)-both in terms of its accuracy and computational cost. We show that SSAIMS can accurately reproduce the AIMS results for the three molecules considered at a much cheaper computational cost, often close to that of TSH. We deduce from these tests that an overlap-based criterion for the stochastic-selection process leads to the best agreement with the reference AIMS dynamics for the smallest average number of TBFs.

Highlights

Simulating the dynamics that molecules undergo after light absorption poses a complete challenge for theoretical chemistry as this implies moving beyond the celebrated Born–Oppenheimer approximation.1,2 Following photoexcitation, molecules are likely to access regions of configuration space where nuclear motion can trigger changes in electronic eigenstates—the so-called nonadiabatic effects—causing a breakdown of the Born–Oppenheimer approximation
We use the photodynamics of three different molecules—cyclopropanone, fulvene, and 1,2-dithiane—to investigate (i) the potential of stochastic-selection AIMS (SSAIMS) to reproduce reference Ab Initio Multiple Spawning (AIMS) results for challenging nonadiabatic dynamics, (ii) the compromise achieved by SSAIMS in obtaining accurate results while using the smallest average number of trajectory basis functions (TBFs) as possible, and (iii) the performance of SSAIMS in comparison to the mixed quantum/classical method trajectory surface hopping (TSH)—both in terms of its accuracy and computational cost
We applied the novel framework of stochasticselection ab initio multiple spawning (SSAIMS) to the challenging photodynamics of different molecular systems to highlight its advantages and limitations and compare its performance with the celebrated mixed quantum/classical method TSH

Summary

Introduction

Simulating the dynamics that molecules undergo after light absorption poses a complete challenge for theoretical chemistry as this implies moving beyond the celebrated Born–Oppenheimer approximation. Following photoexcitation, molecules are likely to access regions of configuration space where nuclear motion can trigger changes in electronic eigenstates—the so-called nonadiabatic effects—causing a breakdown of the Born–Oppenheimer approximation. A typical starting point for developing nonadiabatic molecular dynamics techniques is to express the molecular wavefunction within the Born–Huang representation This representation scitation.org/journal/jcp introduces the common picture of photochemical processes where nuclear wavefunctions evolve on potential energy surfaces and transfer amplitudes between different electronic states during nonradiative relaxation processes. Accurate methods, such as multiconfigurational time-dependent Hartree (MCTDH), express the electronic structure quantities and nuclear wavefunctions on a grid and subsequently allow for a numerically exact solution of the nuclear time-dependent Schrödinger equation for a few tens of nuclear degrees of freedom. One should consider additional approximations to the molecular time-dependent Schrödinger equation to simulate the excited-state dynamics of molecules in their full configurational space

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