Bandstructure study of magnetic and orbital order in BaCoO3

Ab initio calculations were performed in the quasi-one-dimensional BaCoO3 using the FP-APW+lo method as implemented in the WIEN2k package utilizing the LDA+U approach. Several magnetic configurations were studied, exploring different intra- and inter-chain couplings. The most stable configuration is the ferromagnetic low-spin state. The electronic structure of the Co4+ ion (t2g5) has an orbital degree of freedom. When an “alternating-orbital” ordering is allowed along the Co chains, the energy of the system is drastically reduced, whereas the magnetic order is a secondary effect. This orbital ordered state reproduces the experimentally found semiconducting behaviour, which is analysed studying the bandstructure of the material.