Numerical simulations of roughening temperatures in a hexagonal van-der-Waals4He crystal

We have carried out numerical simulations to investigate roughening on4He crystal surfaces. Algorithms were constructed for an h.c.p. crystal, incorporating van-der-Waals interatomic interactions. The Wulff plot was calculated at 0 K. Also, by sectioning the crystal in several symmetry directions, roughening temperatures, TR, have been calculated for these orientations using a lattice-gas model. In particular, these have been determined for thec, a ands facets, as well as for lower-symmetry facets which involve interactions between higher-than-nearest-neighbours. On one of these facets, we have observed the formation of anisotropic clusters below a certain critical temperature. The values for the high-symmetry facets are more precise but in broad agreement with those calculated by Touzani and Wortis1 and do not agree particularly well with the observed values. We are therefore investigating quantum corrections to the calculations.