A study of the valence electron approximation: Application to LiH

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Abstract
Using the valence bond approach and a six-term wave function valence electron calculations are made of the energy and dipole moment of lithium hydride. Comparisons are then made with previous two- and with four-electron results. It is found that reasonable agreement with four-electron calculations of the dipole moment is obtained when the valence orbitals are made orthogonal to the orbitals of the neglected lithium inner shell 1s electrons and that an approximate variational theorem for the energy is then valid. On the other hand, when one fails to require the valence orbitals to be orthogonal to the inner shell an energy lower than the ‘experimental’ energy can be obtained and the computed dipole moment is in poor agreement with the computed four-electron moment and with the experimentally determined moment. Finally, as with four-electron calculations, hybridization with the 2p covalent structure is necessary to give a reasonable dipole moment.

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