Influence of three-body forces and anharmonic effects on the zero-point energy of rare-gas crystals

The stabilization of the fcc structure of the heavier rare-gas crystals is mainly due to the zero-point energy (ZPE) calculated at the harmonic level with two-body contributions only. We evaluate the influence of the anharmonic contributions on the ZPE within the Einstein approximation. For the influence of the three-body contributions we develop an analytic three-body potential fitted to coupled-cluster ab initio data. Both the anharmonic and three-body contributions change the absolute value of the ZPE, but have no influence on the fcc-hcp energy difference.