Electron- and hole-hopping amplitudes in a diatomic molecule. III.porbitals

The dependence of electronic hopping amplitude between neighboring atoms on the charge occupation of the orbitals is studied here for the case of p orbitals. Three different orientations of the orbitals at the two atoms are considered: σ, π, and π’, corresponding to an angle between the orbitals and the line connecting the atoms of 0°, 90°, and 45°, respectively. The Mulliken approximation is found to hold accurately for the π arrangement but not for the σ and π’ arrangements; as a consequence in the latter cases the hopping amplitudes are found to vary with charge occupation even if a single rigid orbital per atom is considered. When modification of atomic orbitals with charge occupation is allowed for and intraatomic radial correlations are considered, the hopping amplitude is found to vary with charge occupation in all three cases, becoming increasingly smaller as more electrons are added. The dependence of our results on the ionic charge Z, and possible implications for the understanding of superconductivity in high-${\mathit{T}}_{\mathit{c}}$ oxides and fullerenes are discussed.