Calculated Elasticity of Al-Bearing Phase D

Using first-principles calculations, this study evaluates the structure, equation of state, and elasticity three compositions phase D up to 75 GPa: (1) magnesium endmember [MgSi2O4(OH)2], (2) aluminum [Al2SiO4(OH)2], (3) with 50% Al-substitution [AlMg0.5Si1.5O4(OH)2]. We find that Mg-endmember undergoes hydrogen-bond symmetrization is linked a 22% increase in bulk modulus D, agreement previous studies. Al2SiO4(OH)2 also symmetrization, but concomitant only 13%—a significant departure from Mg-endmember. Additionally, Al-endmember denser (2%–6%), less compressible (6%–25%), has faster compressional (6%–12%) shear velocities (12%–15%) relative its counterpart. Finally, we investigated properties [AlMg0.5Si1.5O4(OH)2], found state parameters, elastic constants tie-line composition cannot be accurately modeled by interpolating Mg- Al-endmembers.