Ab Initio Molecular Dynamics on the Electronic Boltzmann Equilibrium Distribution

TL;DR

This paper introduces a new molecular dynamics approach that accurately models classical and quantum particles at equilibrium, avoiding adiabatic assumptions and handling potential energy surface crossings, with applications to temperature effects in molecular systems.

Contribution

It develops a dynamics framework for classical particles coupled with quantum populations that naturally incorporates Boltzmann equilibrium without adiabatic assumptions.

Findings

Successfully models temperature effects in degenerate molecular states.

Handles potential energy surface crossings without issues.

Demonstrates application to ozone ring-closure process.

Abstract

We prove that for a combined system of classical and quantum particles, it is possible to write a dynamics for the classical particles that incorporates in a natural way the Boltzmann equilibrium population for the quantum subsystem. In addition, these molecular dynamics do not need to assume that the electrons immediately follow the nuclear motion (in contrast to any adiabatic approach), and do not present problems in the presence of crossing points between different potential energy surfaces (conical intersections or spin-crossings). A practical application of this molecular dynamics to study the effect of temperature in molecular systems presenting (nearly) degenerate states - such as the avoided crossing in the ring-closure process of ozone - is presented.