Isomorphic classical molecular dynamics model for an excess electron in a supercritical fluid

TL;DR

This paper uses ring polymer molecular dynamics to simulate an excess electron in a supercritical fluid, assessing its accuracy across densities and revealing quantum effects on electron diffusion.

Contribution

It introduces a RPMD-based model for electron dynamics in supercritical fluids and evaluates its accuracy against exact path integral methods across different densities.

Findings

RPMD underestimates delocalized states at low densities

Model accuracy improves at higher densities

Quantum dispersion reduces electron self-diffusion in dense fluids

Abstract

Ring polymer molecular dynamics (RPMD) is used to directly simulate the dynamics of an excess electron in a supercritical fluid over a broad range of densities. The accuracy of the RPMD model is tested against numerically exact path integral statistics through the use of analytical continuation techniques. At low fluid densities, the RPMD model substantially underestimates the contribution of delocalized states to the dynamics of the excess electron. However, with increasing solvent density, the RPMD model improves, nearly satisfying analytical continuation constraints at densities approaching those of typical liquids. In the high density regime, quantum dispersion substantially decreases the self-diffusion of the solvated electron. In this regime where the dynamics of the electron is strongly coupled to the dynamics of the atoms in the fluid, trajectories that can reveal diffusive motion of the electron are long in comparison to $\beta\hbar$.