Cluster method for the calculation of the electronic density and the ground-state energy of an insulator: Application to solid helium

Abstract

We propose a new method based on small clusters with the constraint of periodic symmetry to compute electron density and ground-state electronic energy of solids. Calculations are carried out on h.c.p. solid helium, and the Hartree-Fock density is shown to differ from the sum of atomic densities. The correlation energy is responsible for the existence of a small attractive energy per atom, which depends on the lattice parameters. The binding energy per atom cannot be expressed as the sum of two-atom interatomic potentials, but interatomic interactions to higher order must be included. Their effect is to decrease the Van der Waals attraction and to increase the hard-core repulsion.