Generic accommodations of an atom in the Lennard-Jones fcc and hcp rare-gas solids: A computational study

A comprehensive computational analysis of the stable accommodations of an atom in the Lennard-Jones (LJ) face-centered-cubic (fcc) and hexagonal-closest-packed (hcp) lattices is presented. For a wide range of the guest-host LJ interaction parameters and the number of host atoms removed, N, global optimizations are performed to find the minimum energy structures. Stable accommodations are determined using the convex hull of the energy dependence on N. The most stable ground accommodations are mapped onto the guest-host LJ parameter space for the hosts representing the rare-gas solids from Ne to Xe. The radial distribution function analysis is used to classify the structures found as originating from the guest placements in the lattice voids or at the node. Ten generic accommodations are identified for each lattice. Comparing to mostly polyhedral structures in fcc, the hcp ones have generally lower symmetry, which should affect the band shapes of atomic absorption spectra. Despite the well-known wrong prediction of higher hcp phase stability in the LJ model, the cases of strong accommodation preferences in one phase or another are identified. Being generic, the obtained results can be useful for a qualitative interpretation of atomic matrix isolation experiments.