Unrestricted Hartree-Fock approach to cluster calculations. II. Interaction of cluster and environment

An $\mathrm{ab}$ initio approach to determining the appropriate potential in which to embed a cluster in order to simulate a large system is proposed. For ionic and covalent systems, simple approximations are presented as obtained by systematic simplifications of the more general theory. It is also seen that for metallic systems such a reduction is not obtained. The results obtained using the current approach for LiF simulated by a ${\mathrm{Li}}_6$F cluster are contrasted to those obtained using a more conventional Watson-sphere environment and also free-space boundary conditions.