Symmetry-adapted perturbation theory analysis of band structure for a linear H2crystal

Abstract

The physically interpretable contributions to the valence-band energy of the linear H2 crystal models have been calculated by the Musher-Amos-Murrell-Shaw symmetry-adapted perturbation theory. It is shown that the molecular level is shifted by the first- and second-order electrostatic contributions independent of the wavevector k. The second-order electrostatic energy is negligible in comparison to that of the first-order, which is the crystal field effect. The second-neighbour crystal-field contribution can be approximated as the electron-quadrupole interaction. The exchange contributions depend on k. Among them the only practically important term is the first-order exchange energy corresponding to the first-neighbour interaction. The extrapolation of the present results to more complex molecular crystals is discussed.