A Caltech Library Service

Ab initio study of the structure and relative stability of MgSiO₄H₂ polymorphs at high pressures and temperatures

Solomatova, Natalia V. and Caracas, Razvan and Bindi, Luca and Asimow, Paul D. (2022) Ab initio study of the structure and relative stability of MgSiO₄H₂ polymorphs at high pressures and temperatures. American Mineralogist, 107 (5). pp. 781-789. ISSN 0003-004X. doi:10.2138/am-2021-7937.

[img] PDF - Published Version
See Usage Policy.

[img] Archive (ZIP) - Supplemental Material
See Usage Policy.


Use this Persistent URL to link to this item:


Using particle swarm optimization with density functional theory, we identify the positions of hydrogen in a hypothetical Mg-end-member of phase egg (MgSiO₄H₂) and predict the most stable crystal structures with MgSiO₄H₂ stoichiometry at pressures between 0 and 300 GPa. The particle swarm optimization method consistently and systematically identifies phase H as the energetically most stable structure in the pressure range 10–300 GPa at 0 K. Phase Mg-egg has a slightly higher energy compared to phase H at all relevant pressures, such that the energy difference nearly plateaus at high pressures; however, the combined effects of temperature and chemical substitutions may decrease or even reverse the energy difference between the two structures. We find a new MgSiO₄H₂ phase with the P4₃2₁2 space group that has topological similarities to phase Mg-egg and is energetically preferred to phase H at 0–10 GPa and 0 K. We compute the free energies for phase Mg-egg, phase P4₃2₁2, and phase H at 0–30 GPa within the quasi-harmonic approximation and find that the effect of temperature is relatively small. At 1800 K, the stability field of phase P4₃2₁2 relative to the other polymorphs increases to 0–14 GPa, while pure phase Mg-egg remains energetically unfavorable at all pressures. Simulated X-ray diffraction patterns and Raman spectra are provided for the three phases. Additionally, the crystallographic information for two metastable polymorphs with the P1 space group is provided. Our results have implications for the deep hydrogen cycle in that we identify two novel potential carrier phases for hydrogen in the mantles of terrestrial planets and assess their stability relative to phase H. We determine that further experimental and computational investigation of an extended compositional space remains necessary to establish the most stable dense hydrated silicate phases.

Item Type:Article
Related URLs:
URLURL TypeDescription
Solomatova, Natalia V.0000-0002-2331-3427
Caracas, Razvan0000-0003-4586-776X
Bindi, Luca0000-0003-1168-7306
Asimow, Paul D.0000-0001-6025-8925
Alternate Title:Ab initio study of the structure and relative stability of MgSiO4H2 polymorphs at high pressures and temperatures
Additional Information:© 2022 Mineralogical Society of America. Open access: Article available to all readers online. Manuscript received December 21 2020; Manuscript accepted July 7, 2021; Manuscript handled by Bin Chen. This research was supported in part by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement no. 681818–IMPACT to R.C.). We acknowledge access to the Irene supercomputer through the PRACE computing grant no. RA4947 and the PSMN center of ENS Lyon.
Funding AgencyGrant Number
European Research Council (ERC)681818
Partnership for Advanced Computing in Europe (PRACE)RA4947
École Normale Supérieure de LyonUNSPECIFIED
Subject Keywords:Ab initio, global hydrogen cycle, dense hydrous magnesium silicates, lower mantle, high pressure, phase egg, phase H, Physics and Chemistry of Earth’s Deep Mantle and Core
Issue or Number:5
Record Number:CaltechAUTHORS:20220623-426329800
Persistent URL:
Official Citation:Natalia V. Solomatova, Razvan Caracas, Luca Bindi, Paul D. Asimow; Ab initio study of the structure and relative stability of MgSiO4H2 polymorphs at high pressures and temperatures. American Mineralogist 2022; 107 (5): 781–789. doi:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115246
Deposited By: Tony Diaz
Deposited On:24 Jun 2022 21:49
Last Modified:28 Jun 2022 19:08

Repository Staff Only: item control page