Ab initio calculation of band structure, x-ray emission, quantum yield, and electron-energy-loss spectra of hexagonal boron nitride

The band structure of hexagonal boron nitride (BN) has been calculated using an ab initio linear combination of pseudoatomic-orbitals method. The calculated band structure confirms a previous finding that this material is an indirect band-gap insulator and has two empty interlayer bands. Projected densities of states are compared with the experimental x-ray emission spectra of B and N K edges and the agreement is good. This good agreement between the present ground-state calculation and the experimental x-ray emission spectra supports our previous finding that there should be very little valence electron relaxation effect on x-ray emission spectra. A real-space Green's function technique and the Z+1 approximation have been used to calculate the exciton spectra of B and N K edges. The first peak at 192 eV in B K edge is found to be a bound exciton with a binding energy of 1.7±0.4 eV. Only resonance is found for the N K edge. The calculated exciton spectra agree very well with the experimental quantum-yield and electron-energy-loss spectra.