The structure and elasticity of phase B silicates under high pressure by first principles simulation

Abstract

The structures and elasticities of phase B silicates with different water and iron (Fe) content are obtained by firstprinciples simulation to understand the effects of water and Fe on their properties under high pressure. The lattice constants a and b decrease with increasing water content. On the contrary, c increases with increasing water content. On the other hand, the b and c decrease with increasing Fe content while a increases with increasing Fe content. The decrease of M (metal)-O octahedral volume is greater than the decrease of SiO polyhedral volume over the same pressure range. The density, bulk modulus and shear modulus of phase B increase with increasing Fe content and decrease with increasing water content. The compressional wave velocity (V p ) and shear wave velocity (V s ) of phase B decrease with increasing water and Fe content. The comparisons of density and wave velocity between phase B silicate and the Earth typical structure provide the evidence for understanding the formation of the X-discontinuity zone of the mantle.

The Structure and Elasticity of CaO3 Under High Pressure by First-Principles Simulation

“…To further verify the validity of our calculation approach, the O-O bond length and bond angle of the O-O-O bond were calculated under 0-50 GPa (Figure 1) and compared with the Those slight differences between our calculated values with previous results are mainly due to the calculated temperature difference and the insufficient binding energy of GGA (Liu et al, 2018). Therefore, the general agreement of our calculations with previous results demonstrates the validity of our computational method and its ability to reproduce the properties of CaO 3 .…”

Detailed structural, mechanical, and electronic study of five structures for CaF2 under high pressure*

“…In recent years, much theoretical works focused on phase transition under high pressure were done by CASTEP. [35][36][37][38] Moreover, the thermodynamic properties of CaF 2 were calculated with an approximation method on the quasi-harmonic Debye model. [39] In order to get more accurate theoretical results, two different forms of exchange-correlation (XC) energy are treated: one is generalized gradient approximation (GGA) in the Perdew-Burke-Ernzerhof (PBE) [40] functional form, and the other one is local spin density approximation (LDA) proposed by Ceperley and Alder [41] and parametrized by Perdew and Zunder [42] (CA-PZ).…”