First-principles calculations of the ferroelastic transition between rutile-type andCaCl2-typeSiO2at high pressures

Abstract

The tetragonal to orthorhombic ferroelastic phase transition between rutile- and ${\text{CaCl}}_2$-type ${\text{SiO}}_2$ at high pressures is studied using first-principles calculations and the Landau free-energy expansion. The phase transition is systematically investigated in terms of characteristic phonon modes with ${\text{B}}_{1g}$ and ${\text{A}}_g$ symmetries, shear moduli, transverse-acoustic mode, rotation angle of the ${\text{SiO}}_6$ octahedra, spontaneous symmetry-breaking and volume strains, and enthalpy. The results show that these physical behaviors at the transition are well described using the Landau free-energy expansion parametrized by the first-principles calculations.