Nature of the Metallization Transition in Solid Hydrogen

TL;DR

This study uses advanced quantum Monte Carlo methods to investigate the electronic band gaps of high-pressure solid hydrogen, revealing that metallization likely occurs through a structural phase transition rather than simple band gap closure.

Contribution

The paper provides the first accurate DMC calculations of excitonic and quasiparticle gaps in various hydrogen structures at high pressures, highlighting the importance of nuclear quantum effects.

Findings

Metallization occurs via a structural phase transition.

Nuclear quantum effects significantly influence electronic structure.

Many-body gaps can be estimated using a size-independent scissor correction.

Abstract

We present an accurate study of the static-nucleus electronic energy band gap of solid molecular hydrogen at high pressure. The excitonic and quasiparticle gaps of the $C2/c$, $Pc$, $Pbcn$, and $P6_3/m$ structures at pressures of 250, 300, and 350~GPa are calculated using the fixed-node diffusion quantum Monte Carlo (DMC) method. The difference between the mean-field and many-body band gaps at the same density is found to be almost independent of system size and can therefore be applied as a scissor correction to the mean-field gap of an infinite system to obtain an estimate of the many-body gap in the thermodynamic limit. By comparing our static-nucleus DMC energy gaps with available experimental results, we demonstrate the important role played by nuclear quantum effects in the electronic structure of solid hydrogen. Our DMC results suggest that the metallization of high-pressure solid hydrogen occurs via a structural phase transition rather than band gap closure.