Prediction of possible CaMnO₃ modifications using an ab initio minimization data-mining approach

We have performed a crystal structure prediction study of CaMnO₃ focusing on structures generated by octahedral tilting according to group-subgroup relations from the ideal perovskite type (), which is the aristotype of the experimentally known CaMnO₃ compound in the Pnma space group. Furthermore, additional structure candidates have been obtained using data mining. For each of the structure candidates, a local optimization on the ab initio level using density-functional theory (LDA, hybrid B3LYP) and the Hartree--Fock (HF) method was performed, and we find that several of the modifications may be experimentally accessible. In the high-pressure regime, we identify a post-perovskite phase in the CaIrO₃ type, not previously observed in CaMnO₃. Similarly, calculations at effective negative pressure predict a phase transition from the orthorhombic perovskite to an ilmenite-type (FeTiO₃) modification of CaMnO₃.