Anisotropy of chemical bond and electronic structure in graphite-like and orthorhombic boron nitride

Zone spectra, densities of valent charge and level of electrical neutrality are calculated using pseudopotential method in graphite-like (h-BN) and orthorhombic (r-BN) modifications of boron nitride. The given compounds are shown to be indirect-zone isolators with minimal energies of indirect (4.65 and 4.8 eV) and direct (5.27 and 5.5 ev) forbidden zone in h-and r-BN, respectively. Zone energies of h-BN agree with the experimental data. Chemical bond in both crystals is similar and is of mixed ion-covalent character. 36 refs., 7 figs., 4 tabs