Abstract
The Direct Dynamics variational Multi-Configurational Gaussian (DD-vMCG) method provides a fully quantum mechanical solution to the time-dependent Schrödinger equation for the time evolution of nuclei with potential surfaces calculated on-the-fly using a quantum chemistry program. Initial studies have shown its potential for flexible and accurate simulations of non-adiabatic excited-state molecular dynamics. In this paper, we present developments to the DD-vMCG algorithm that improve both its accuracy and efficiency. First, a new, efficient parallel algorithm to control the DD-vMCG database of quantum chemistry points is presented along with improvements to the Shepard interpolation scheme. Second, the use of symmetry in describing the potential surfaces is introduced along with a new phase convention in the propagation diabatization. Benchmark calculations on the allene radical cation including all degrees of freedom then show that the new scheme is able to produce a consistent non-adiabatic coupling vector field. This new DD-vMCG version thus opens the route for effectively and accurately treating complex chemical systems using quantum dynamics simulations.
Highlights
Quantum molecular dynamics simulations are essential to understand a number of different phenomena, especially those occurring on the ultra-fast, femtosecond time scale, where simulations are necessary to interpret experimental data
The first part of this study was to improve the efficiency of a Direct Dynamics variational Multi-Configurational Gaussian (DD-variational Multi-Configurational Gaussian (vMCG)) simulation by optimizing the use of the quantum chemistry (QC) database used to obtain the potential surfaces by Shepard interpolation
From the results above it is clear that the DD-vMCG method is able to provide good quality diabatic surfaces for multi-dimensional non-adiabatic simulations directly from a set of quantum chemistry calculations
Summary
Quantum molecular dynamics simulations are essential to understand a number of different phenomena, especially those occurring on the ultra-fast, femtosecond time scale, where simulations are necessary to interpret experimental data. This includes fundamental dynamical processes in chemistry, such as photodissociation [1,2,3,4] or proton transfer [5,6,7,8]. The Born-Oppenheimer approximation separates the electronic and nuclear motions, and the nuclei move on potential energy surfaces provided by the electrons [10,11,12,13,14]. For an N atom molecular system, the potential energy surfaces are a function of the 3N nuclear Cartesian coordinates, which is completely described by 3N -6 linearly independent internal coordinates (3N -5 for a linear molecule), as the Hamiltonian is invariant to rotation and translation of the entire system
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