Nuclear quantum effects induce metallization of dense solid molecular hydrogen. Issue 5 (8th November 2017)

• Record Type: Journal Article
• Authors: Azadi, Sam; Singh, Ranber; Kühne, Thomas D.
• Is Part Of: Journal of computational chemistry. Volume 39:Issue 5(2018)
• Page Start: 262
• Page End: 268
• Publication Date: 2017-11-08
• Subjects: metallic hydrogen -- nuclear quantum effects -- path‐integral molecular dynamics -- Car‐Parrinello molecular dynamics -- quantum Monte Carlo; Chemistry -- Data processing -- Periodicals; 542.85
• DOI: 10.1002/jcc.25104
• Languages: English
• ISSNs: 0192-8651

Abstract

Abstract : We present an accurate computational study of the electronic structure and lattice dynamics of solid molecular hydrogen at high pressure. The band‐gap energies of the C 2 / c, Pc, and P 6 3 / m structures at pressures of 250, 300, and 350 GPa are calculated using the diffusion quantum Monte Carlo (DMC) method. The atomic configurations are obtained from ab initio path‐integral molecular dynamics (PIMD) simulations at 300 K and 300 GPa to investigate the impact of zero‐point energy and temperature‐induced motion of the protons including anharmonic effects. We find that finite temperature and nuclear quantum effects reduce the band‐gaps substantially, leading to metallization of the C 2 / c and Pc phases via band overlap; the effect on the band‐gap of the P 6 3 / m structure is less pronounced. Our combined DMC‐PIMD simulations predict that there are no excitonic or quasiparticle energy gaps for the C 2 / c and Pc phases at 300 GPa and 300 K. Our results also indicate a strong correlation between the band‐gap energy and vibron modes. This strong coupling induces a band‐gap reduction of more than 2.46 eV in high‐pressure solid molecular hydrogen. Comparing our DMC‐PIMD with experimental results available, we conclude that none of the structures proposed is a good candidate for phases III and IV of solid hydrogen. © 2017 Wiley Periodicals, Inc. Abstract : Combined ab initio PIMD and DMC simulations suggest that finite‐temperature and nuclear quantum effects entails a band‐gap reduction of at least 2.5 eV. As this renders all candidate structures, we have considered here metallic, which is in contrast with available experimental measurements, we conclude that none of the proposed structures are likely candidates for phase III and IV of solid molecular hydrogen.