Abstract: The structure and elastic properties of MgSiO₃, a major mantle-forming phase, have been simulated using computer models which predict the minimum energy structure by using interatomic pair potentials to describe the net forces acting between the atoms. Four such interatomic potentials were developed in this study, and are compared with potential N1 of Miyamoto and Takeda (1984). The most successful potential (W3) was derived by fitting the short range potential parameters to both the experimentally obtained structural and elastic properties of MgSiO₃ perovskite. The relative stabilities of some of the possible perovskite polymorphs, the orthorhombic, cubic, and tetragonal phases and hexagonal polytypes, were evaluated at 0 K and between 1 bar and 2 Mbar. The orthorhombic phase is found to be stable at all but the highest pressures, where the cubic phase may be stable. The temperature of the ortho-rhombic to cubic transition may decrease with increasing pressure. The energy of a stacking fault on (110) in the cubic phase was estimated using the ANNNI model and found to be about 1.95 J m⁻² using potential W3. The distance of separation of partial dislocations of this type is predicted to increase with increasing pressure from 8.4 Å at 1 bar to 9.2 Å at 1 Mbar.