Origin of octahedral tilting in orthorhombic perovskites

The adopted crystal structure of the ABO₃ perovskites is determined by the balance between the interaction of the semicore states of the A and B atoms and oxygen ions. Topological considerations show that the structural setup always stabilizes the cubic phase at large pressures, while small or negative pressures favor nonvanishing octahedral tiltings. As an example, we show that the structural distortion in CaSiO₃ perovskite is slightly depressed with hydrostatic pressure, but it increases significantly with increasing volume.