BaCoO3 monoclinic structure and chemical bonding analysis: hybrid DFT calculations

Abstract

Cobalt based perovskites have great potential for numerous applications. Contrary to a generally assumed hexagonal space group (SG P6₃/mmc) model as the ground state of BaCoO₃ (BCO), our hybrid DFT calculations with B1WC density functional and the symmetry group–subgroup derived crystal structure model support the ground state of BCO to be indeed monoclinic, in agreement with recent experimental predictions [Chin et al., Phys. Rev. B, 2019, 100, 205139]. We found for the monoclinic BCO that the C-type anti-ferromagnetic low-spin (AFM LS) state (SG P2/c) is energetically only slightly more preferential at 0 K than the ferromagnetic (FM) LS state (SG C2/c). In turn, these monoclinic structures are energetically more favourable than the hexagonal ones, due to slight z-axis tilting. The analysis of density of states (DOS) and crystal orbital overlap population (COOP) shows a significant (almost 2 eV) separation between occupied and empty t_2g states (in the spin-down channel and corresponding anti-bonding states) induced by the z-axis tilting.