Minimizing the time-dependent density functional error in Ehrenfest dynamics

TL;DR

This paper compares two methods of simulating electron-ion dynamics using time-dependent density functional theory within Ehrenfest dynamics, highlighting that propagating electronic coefficients on linear-response surfaces yields more accurate results with approximate functionals.

Contribution

The study demonstrates that propagating electronic coefficients on linear-response surfaces is more accurate than propagating Kohn-Sham equations when using approximate functionals in Ehrenfest dynamics.

Findings

Linear-response surface propagation is more accurate with approximate functionals.

Different approaches yield qualitatively different dynamics.

Implications for time-resolved spectroscopy are discussed.

Abstract

Simulating electron-ion dynamics using time-dependent density functional theory within an Ehrenfest dynamics scheme can be done in two ways that are in principle exact and identical: propagating time-dependent electronic Kohn-Sham equations or propagating electronic coefficients on surfaces obtained from linear-response. We show here that using an approximate functional leads to qualitatively different dynamics in the two approaches. We argue that the latter is more accurate because the functionals are evaluated on domains close to the ground-state where current approximations perform better. We demonstrate this on an exactly-solvable model of charge-transfer, and discuss implications for time-resolved spectroscopy.