An investigation into the approximations used in wave packet molecular dynamics for the study of warm dense matter

TL;DR

This paper critically examines key approximations in wave packet molecular dynamics (WPMD) for warm dense matter, demonstrating that semi-empirical corrections improve accuracy but reducing reliance on scaling enhances physical insight.

Contribution

The study identifies the impact of basis set restrictions, exchange, and correlation approximations in WPMD and proposes a semi-empirical correction with a two Gaussian basis for better accuracy.

Findings

Combining a two Gaussian basis with a semi-empirical correction improves WPMD accuracy.

Semi-empirical scaling parameters are essential but can be minimized for more physics-based results.

The correction parameter can be tuned to match experimental pressures in dense hydrogen.

Abstract

Wave packet molecular dynamics (WPMD) has recently received a lot of attention as a computationally fast tool to study dynamical processes in warm dense matter beyond the Born-Oppenheimer approximation. These techniques, typically, employ many approximations to achieve computational efficiency while implementing semi-empirical scaling parameters to retain accuracy. We investigate three of the main approximations ubiquitous to WPMD: a restricted basis set, approximations to exchange, and the lack of correlation. We examine each of these approximations in atomic and molecular hydrogen in addition to a dense hydrogen plasma. We find that the biggest improvement to WPMD comes from combining a two Gaussian basis with a semi-empirical correction based on the valence-bond wave function. A single parameter scales this correction to match experimental pressures of dense hydrogen. Ultimately, we find that semi-empirical scaling parameters are necessary to correct for the main approximations in WPMD. However, reducing the scaling parameters for more ab-initio terms gives more accurate results and displays the underlying physics more readily.