Magnetic, Electronic, and Optical Properties of the Tetraborates NiB4O7 and CoB4O7 in Three Structural Modifications

The physical properties of the NiB4O7 and CoB4O7 tetraborate compounds in three structural modifications with the sp. gr. Pbca, Cmcm, and P6522 have been calculated using the density functional theory in the VASP software package. The pressure dependences of the enthalpy of the compounds in the investigated structural modifications have been calculated. The calculated electron densities of states and band structures showed that the compounds under study in all the considered modifications are dielectrics with a band gap of 3–4 eV. The calculation of the magnetic exchange constants in the Heisenberg model have shown qualitative agreement with the experiment.