Effect of overlap of localized orbitals on the band structure of insulators under pressure

A new method for calculating the energy spectra of compressed insulators based on the cluster expansion is proposed. The dependence on the compression of the spectra of both the conduction band and the valence bands is uniquely determined by the values of the overlap integrals of the orbitals of pairs of isolated atoms. The overlap integrals and the matrices defined by them are calculated numerically for inert-gas crystals and their properties and values are analyzed for different lattice constants. Numerical calculations of the bands of the compressed crystal in the various proposed models are carried out and discussed for neon.