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

Cohesive properties of the NaF crystal have been calculated by evaluation of the electrostatic, valence repulsion, induction, and dispersion contributions. All quantities have been computed with an accuracy up to S 2 terms using high quality Hartree-Fock wavefunctions for the Na + and F - ions. Two- and three-body forces as well as the nearest- and the next-nearest-neighbour exchange interactions have been considered. The role of further neighbour interactions has been estimated. The results are in satisfactory agreement with the experimental data.