The stability of cubic ${\mathrm{CaSiO}}_3$ perovskite with respect to octahedral rotations is investigated by ab initio total-energy calculations. The proposed theoretical ground-state crystal structure has the orthorhombic Pbnm symmetry. Pressure gradually reduces the average tilting of the ${\mathrm{SiO}}_6$ octahedra relative to the cubic axis, from 7° at zero pressure to 4° at about 150 GPa. The energy difference between the orthorhombic and cubic phases at 0 GPa is 63 meV per f.u. and shows weak pressure dependence. A possible stabilization of the cubic phase at finite temperatures by entropy effects is discussed.

• Received 28 February 2002

DOI:https://doi.org/10.1103/PhysRevB.65.193107