Importance of exchange effects in the deformation of interacting ions

In calculations for liquids or solids one often considers a limited cluster of atoms or molecules in the electrostatic field of their environment. In this paper possibilities of improving this model by inclusion of the exchange deformation potential are shown. The reported numerical results for the LiF and NaF molecules as well as for the LiF and NaF perfect crystals indicate the importance of the exchange deformation effects.