Theoretical Study of Alkali-Metal Hydrides at High Pressures: A Case of NaH Supported by Inelastic Neutron Scattering (INS) Experiments at 1 and 2 GPa

Anup Pandey, Jiayong Zhang, Yongqiang Cheng, Luke Daemen, Anibal J. Ramirez-Cuesta

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1 Scopus citations

Abstract

Pressure-induced effects in alkali hydrides are investigated using a plane-wave density functional theory method. For the first time, we have measured the inelastic neutrons scattering (INS) spectra of NaH at pressures 1 and 2 GPa and used it to validate INS simulated from the first-principles calculations using both local density approximation (LDA) and the generalized gradient approximation (GGA). We found that LDA describes lattice dynamics better compared to the GGA. Thermodynamic properties such as lattice parameters, bulk modulus, and their derivatives are calculated using full lattice dynamics theory within the quasi-harmonic approximation (QHA) for all alkali hydrides. Anharmonic effects are investigated for NaH from the molecular dynamics trajectories and are negligible at given temperature and pressures. We have shown that the phase-change pressures obtained from the equal Gibbs free-energy conditions for two phases compare well with the available experimental data and is the accurate phase-change criterion. This study corroborates INS as an important complementary tool in benchmarking first-principles calculations.

Original languageEnglish
Pages (from-to)10079-10085
Number of pages7
JournalJournal of Physical Chemistry A
Volume123
Issue number46
DOIs
StatePublished - Nov 21 2019

Funding

Neutron scattering experiments were performed at the VISION beamline at Oak Ridge National Laboratory’s Spallation Neutron Source (SNS), which is supported by the Scientific User Facilities Division, Office of Basic Energy Sciences (BES), U.S. Department of Energy (DOE), under contract no. DE-AC0500OR22725 with UT-Battelle, LLC. This work was a part of the ICEMAN project funded by the Laboratory Directed Research and Development (LDRD 8237) at ORNL. This work used the resources of Oak Ridge Leadership Facility (OLCF) for the computational work, available through the VirtuES (Virtual Experiments in Spectroscopy) project, funded by Laboratory Directed Research and Development program.

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