Velocity autocorrelations across the molecular-atomic fluid transformation in hydrogen under pressure

TL;DR

This study investigates how velocity autocorrelations change during the molecular to atomic fluid transition in hydrogen under pressure, revealing complex dynamics and a vibrational mode crossover through ab initio molecular dynamics simulations.

Contribution

It provides detailed analysis of velocity autocorrelation functions and diffusion coefficients across the transition, highlighting vibrational mode behavior and the molecular-atomic transformation.

Findings

Non-monotonous velocity autocorrelation changes observed

Diffusion coefficients measured across a wide density range

Crossover in vibrational density of intramolecular modes identified

Abstract

Non-monotonous changes in velocity autocorrelations across the transformation from molecular to atomic fluid in hydrogen under pressure are studied by ab initio molecular dynamics simulations at the temperature 2500 K. We report diffusion coefficients in a wide range of densities from purely molecular fluid up to metallic atomic fluid phase. An analysis of contributions to the velocity autocorrelation functions from the motion of molecular centers-of-mass, rotational and intramolecular vibrational modes is performed, and a crossover in the vibrational density of intramolecular modes across the transition is discussed.