Electronic energy gap closure and metal-insulator transition in dense liquid hydrogen

TL;DR

This study uses Quantum Monte Carlo calculations to analyze the insulator-metal transition in dense liquid hydrogen, revealing the nature of the transition and providing insights into electronic properties near the critical point.

Contribution

The paper presents the first detailed QMC analysis of the electronic gap closure and phase transition in dense liquid hydrogen, highlighting differences from DFT predictions.

Findings

Gap closes abruptly below the critical temperature, indicating a weak first-order transition.

Above the critical temperature, molecular dissociation occurs while the gap remains open.

QMC yields larger fundamental gaps and more accurate density of states compared to DFT.

Abstract

Using Quantum Monte Carlo (QMC) calculations, we investigate the insulator-metal transition observed in liquid hydrogen at high pressure. Below the critical temperature of the transition from the molecular to the atomic liquid, the fundamental electronic gap closure occurs abruptly, with a small discontinuity reflecting the weak first-order transition in the thermodynamic equation of state. Above the critical temperature, molecular dissociation sets in while the gap is still open. When the gap closes, the decay of the off-diagonal reduced density matrix shows that the liquid enters a gapless, but localized phase: there is a cross-over between the insulating and the metallic liquids. Compared to different DFT functionals, our QMC calculations provide larger values for the fundamental gap and the electronic density of states close to the band edges, indicating that optical properties from DFT potentially benefit from error cancellations.