Mixed approach of linear-combination-of-atomic-orbitals and orthogonalized-plane-wave methods to the band-structure calculation of alkali-halide crystals

The energy-band structure of lithium chloride, sodium chloride, and potassium chloride has been calculated following a mixed approach of linear-combination-of-atomic-orbitals method for the valence bands and orthogonalized-plane-wave method for the conduction bands. The interpolation scheme developed by Slater and Koster has been used to calculate the matrix elements of the energy operator and the overlap integrals. The influence of the mode of admixture of wave functions to the crystal orbitals is extensively studied. For the different mode of admixture of states, the variations in the band parameters, viz. band gaps, widths, and locations, are noted. The calculated values are compared with experiments and the previous theoretical results.