Ab initio calculation of cohesion energy, compressibility and density of the LiF crystal

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Abstract
Properties of the LiF crystal have been calculated ab initio by taking into account the electrostatic and valence repulsion as well as induction and dispersion effects. The calculations have been carried out with an accuracy up to S2 terms. Two- and three-ion forces have been considered and the valence repulsion of the nearest- and next-nearest neighbours have been computed. All terms have been obtained by using those wavefunctions for the ions which give the expectation values of the energy very close to the corresponding Hartree-Fock limits. The results show that the induction and dispersion effects are of great importance. The computed lattice parameter (4.04 AA), density (2.65 g cm-3), compressibility (1.44*10-12 cm2 dyn-1) and cohesion energy (-244.9 kcal mole-1) agree well with the experimental values of 4.01-4.03 AA, 2.646 g cm-3, 1.43*10-12 cm2 dyn-1 and -246.8+or-2.1 kcal mole-1, respectively.