ROUGHENING TRANSITIONS AND SURFACE-TENSION IN AN HCP LATTICE WITH HIGHER NEIGHBOR INTERACTIONS

We report on Ising lattice-gas simulations of surfaces of a hexagonal- close-packed (hcp) crystal as a function of temperature and higher nei ghbor interactions using sample sizes up to 160 x 160 x 40 sites. The hcp lattice represents He-4 on which three roughening transitions have been observed experimentally. Most previous simulation studies on rou ghening transitions were performed for other lattices where fewer expe rimental data are available. We calculated roughening temperatures for these three surfaces as a function of higher neighbor interactions of both signs. We also calculated the surface tension of the three facet s. In most cases good qualitative (and reasonable quantitative) agreem ent with experiment was found with appropriate values of interactions, confirming the basic validity of the model as applied to surface roug hening.