EAPSI: Evaluating the Melting and Vibrational Properties of Phase H as a Function of Pressure

Thompson Elizabeth C, Chicago IL

Investigators

Abstract

Forty years of scientific literature on the topic has produced wildly variable estimates of the water content within the deep Earth--with values ranging from a quarter to four times the volume of water found in Earth's oceans. The recent discovery of hydrous 'phase H' (MgSiO4H2) provides a new insight into the distribution of water in the Earth's interior. Determining the stability of hydrous phases such as phase H aids in constraining the quantity of water in the lower mantle, a region of the Earth almost 100 times more massive than the crust. The formation of phase H was first predicted in a computational study by Dr. Jun Tsuchiya of the Geodynamics Research Center (GRC) at the University of Ehime, Japan. Dr. Tsuchiya will lend her expertise using first-principles techniques to study high-pressure hydrous phases to this project and the GRC will provide use of a supercomputer that will enable the timely completion of this project. This proposal aims to provide critical insight into the deep Earth's hydrogen budget via three ab initio investigations into key hydrous mantle phases: (1) modeling the melting behavior of phase H as a function of pressure, (2) modeling the melting curve of d-AlOOH, and (3) first-principles calculations of the vibrational properties of phase H as a function of pressure. The melting curves of phase H and d-AlOOH will be determined using a first principles molecular dynamics technique. This type of calculation enables the determination of thermodynamic properties by numerically modeling the interatomic potentials between particles in the system of interest. Vibrational properties of phase H will be calculated using first-principles calculations based on a generalized gradient approximation to the exchange-correlation functional. These calculations are complementary to the principal investigator?s experimental efforts to investigate hydrous phases under extreme conditions and will help constrain the water budget of the Earth's deep interior. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Japan Society for the Promotion of Science.