title: The refractive index and electronic gap of water and ice increase with increasing pressure.
abstract: Determining the electronic and dielectric properties of water at high pressure and temperature is an essential prerequisite to understand the physical and chemical properties of aqueous environments under supercritical conditions, for example, in the Earth interior. However, optical measurements of compressed ice and water remain challenging, and it has been common practice to assume that their band gap is inversely correlated with the measured refractive index, consistent with observations reported for hundreds of materials. Here we report ab initio molecular dynamics and electronic structure calculations showing that both the refractive index and the electronic gap of water and ice increase with increasing pressure, at least up to 30 GPa. Subtle electronic effects, related to the nature of interband transitions and band edge localization under pressure, are responsible for this apparently anomalous behaviour.
authors.affiliation: Department of Chemistry, University of California, Davis, California 95616, USA.
authors.forename: Ding
authors.initials: D
authors.lastname: Pan
authors.affiliation: 1] Department of Chemistry, University of California, Davis, California 95616, USA [2] The Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Quan
authors.initials: Q
authors.lastname: Wan
authors.affiliation: The Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Giulia
authors.initials: G
authors.lastname: Galli