Charge density wave in hydrogen at high pressure

TL;DR

This paper reports MD simulations of hydrogen at high pressure, revealing a new phase characterized by charge density waves and emphasizing the importance of k-point sampling accuracy.

Contribution

It introduces a novel hydrogen phase with charge density wave features and highlights the significance of k-point sampling in MD simulations.

Findings

Discovery of a new hydrogen phase with twofold coordinated chains

Identification of charge density wave as the electronic structure of the phase

Demonstration of the critical role of k-point sampling in simulation accuracy

Abstract

We present extensive molecular dynamics (MD) simulations investigating numerous candidate crystal structures for hydrogen in conditions around the present experimental frontier (400GPa). Spontaneous phase transitions in the simulations reveal a new structure candidate comprising twofold coordinated chains of hydrogen atoms. We explain the electronic structure of this phase in terms of a charge density wave and calculate its experimental signature. In detailed tests of the accuracy of our calculation, we find that k-point sampling is far more important in MD than in static calculations, because of the freedom it give the atoms to rearrange themselves optimally for the given sampling.