Corrections to scaling and self-duality in the restricted solid-on-solid model

The corrections to scaling at and above the roughening transition TR in the restricted solid-on-solid model are studied by means of finite-size scaling for semi-infinite strips of width 2 to 10. It is shown that at a temperature TSD not far above the roughening temperature, where the restricted solid-on-solid model is invariant under the duality transformation of the five-state clock model, the fugacity of the sine-Gordon operator must vanish. For the dual truncated planar model this means that the core energy of the vortices diverges. Between TS and TR the corrections to scaling do not reach their asymptotic behaviour, but are dominated by the contributions from the ( Delta phi )4 operator associated with the restriction to steps of height one.