Ab-initio DFT＋U study on the electronic correlation in multiferroic XY-antiferromagnetic Ba2CoGe2O7

Ab-initio density functional theory (DFT)＋U has been used to study the spin-resolved electronic band structure and the partial density of states of the multiferroic XY-antiferromagnetic Ba2CoGe2O7. Using the constrained random-phase approximation (cRPA) method, the value of Hubbard U and Hund’s coupling JH has been determined and plugged into the further dynamical mean field theory (DMFT) calculations. The strong metal-ligand hybridization between Co-3d and O-2p orbitals in the CoO4 tetrahedron has been demonstrated via DFT and DFT＋DMFT calculations. The calculated indirect band gap in the antiferromagnetic state without and with U (=5 eV) correction is found to be 0.67 and 2.71 eV, respectively. The highest calculated ordered magnetic moment of 2.7 μB/Co2+ is close to the reported experimental value. The presented DFT calculations based on the different orbital models brings the underlying strong electronic correlation in the Ba2CoGe2O7.