SCIENCE@home

Ab initio spectroscopy and ionic conductivity of water under Earth mantle conditions

V. Rozsa,D. Pan,F. Giberti,G. Galli

Published 2018 in Proceedings of the National Academy of Sciences of the United States of America

ABSTRACT

Significance Despite more than a century of study, the properties of water at high pressure and temperature remain difficult to measure. First-principles computations are ideal tools to study matter under extreme conditions, as they require neither assumptions about chemical bonds nor experimental data for fitting interatomic potentials. Here we carry out first-principles simulations to study the diffusivity, vibrational properties, and conductivity of water in a controversial region of its phase diagram (1,000 K, 10–20 GPa). Our results provide insight into water’s dissociation mechanism, the origin of its large ionic conductivity, and the spectroscopic signatures of ionic species. We predict Raman and infrared spectra at several conditions, which will serve as a guide for future experiments. The phase diagram of water at extreme conditions plays a critical role in Earth and planetary science, yet remains poorly understood. Here we report a first-principles investigation of the liquid at high temperature, between 11 GPa and 20 GPa—a region where numerous controversial results have been reported over the past three decades. Our results are consistent with the recent estimates of the water melting line below 1,000 K and show that on the 1,000-K isotherm the liquid is rapidly dissociating and recombining through a bimolecular mechanism. We found that short-lived ionic species act as charge carriers, giving rise to an ionic conductivity that at 11 GPa and 20 GPa is six and seven orders of magnitude larger, respectively, than at ambient conditions. Conductivity calculations were performed entirely from first principles, with no a priori assumptions on the nature of charge carriers. Despite frequent dissociative events, we observed that hydrogen bonding persists at high pressure, up to at least 20 GPa. Our computed Raman spectra, which are in excellent agreement with experiment, show no distinctive signatures of the hydronium and hydroxide ions present in our simulations. Instead, we found that infrared spectra are sensitive probes of molecular dissociation, exhibiting a broad band below the OH stretching mode ascribable to vibrations of complex ions.

PUBLICATION RECORD

CITATION MAP

EXTRACTION MAP

CLAIMS

  • No claims are published for this paper.

CONCEPTS

  • No concepts are published for this paper.

REFERENCES

Showing 1-56 of 56 references · Page 1 of 1

CITED BY

Showing 1-45 of 45 citing papers · Page 1 of 1