We review results obtained with a restricted solid-on-solid model, the so-called FCSOS model, introduced to describe the thermal disordering of fcc (111) crystal surfaces. In the FCSOS, parallel surface steps repel each other, while antiparallel steps do not interact. The model shows a preroughening transition into a disordered flat (DOF) phase, where the outermost surface layer — exposing one of the three sublattices — is half-filled. It is found that a fairly extended parallel-step repulsion is essential to obtain a stable DOF phase. Static as well as dynamical properties obtained with the FCSOS model are reviewed. A close similarity emerges between roughening and preroughening, which is like roughening at a single temperature. The relevance of these results to observations on Ar(111) and other surfaces is briefly discussed.
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