We predict the phase diagram of $\mathrm{Ca}\mathrm{Si}{\mathrm{O}}_3$ perovskite, finding the tetragonal $I4∕mcm$ structure transforming to cubic $Pm\overline{3}m$ with increasing temperature. The transition temperature is $1150\mathrm{K}$ at $0\mathrm{GPa}$, and $2450\mathrm{K}$ at $140\mathrm{GPa}$. The $c∕a$ ratio of the tetragonal structure is 1.018 at $100\mathrm{GPa}$ and increases on compression, as does the static enthalpy difference between tetragonal and cubic structures. The elastic constants of the tetragonal phase at static conditions differ substantially from those of the cubic phase with the Voigt-Reuss-Hill shear modulus 29% less at $100\mathrm{GPa}$. Computations are based on density functional theory in the local density and generalized gradient approximations. The phase diagram and high temperature elastic constants are computed using a mean field theory with parameters of the Landau potential determined via structurally constrained density functional theory calculations. We present a simple scheme for systematically searching for the ground state over all perovskite structures derivable from octahedral rotations within the context of symmetry-preserving relaxation, which confirms tetragonal $I4∕mcm$ as the ground state in density functional theory. We argue that the experimental x-ray diffraction pattern can be explained by the $I4∕mcm$ phase by considering the development of preferred orientation under uniaxial compression.

• Received 22 June 2006

DOI:https://doi.org/10.1103/PhysRevB.75.024108