Spin state and phase stability of iron-bearing Mg2SiO4

Under the extreme conditions of super-Earths interior, MgSiO3 post-perovskite, the last stable silicate phase in the earths mantle, is predicted to dissociate into Mg2SiO4 and SiO2 (Wu et al., 2013; Umemoto et al., 2017). It is the main mantle silicate in super-Earths and recombines with and dissociates into other silicates and oxides. Therefore, it is important to understand the properties of the Mg2SiO4 phases, especially in solid solution with iron. Here we present an ab initio study on the electronic, structural, and vibrational properties of Fe-bearing Mg2SiO4. We study the stability of (Mg2-xFex)SiO4, (Mg2-xFex)Mg(Si1-x/2Fex/2)O4and Mg(Si1-xFex)O4 phases. These results will be useful for modeling the mantle of those super-Earth-type exoplanets. *Research supported by NSF award EAR-1918126 Wu, S. Q., Ji, M., Wang, C. Z., Nguyen, M. C., Zhao, X., Umemoto, K., Wentzcovitch, R. M., & Ho, K. M. (2013). An adaptive genetic algorithm for crystal structure prediction. Journal of Physics: Condensed Matter, 26(3), 035402. https://doi.org/10.1088/0953-8984/26/3/035402 Umemoto, K., Wentzcovitch, R. M., Wu, S., Ji, M., Wang, C. Z., & Ho, K. M. (2017). Phase transitions in MgSiO3 post-perovskite in super-Earth mantles. Earth and Planetary Science Letters, 478, 4045. https://doi.org/10.1016/j.epsl.2017.08.032