  We report large scale Monte Carlo simulations of the equilibrium discrete
Laplacian roughening (dLr) model, originally introduced as the simplest one
accommodating the hexatic phase in two-dimensional melting. The dLr model is
also relevant to surface roughening in molecular beam epitaxy (MBE). Our data
suggest a single phase transition, possibly of the Kosterlitz-Thouless type,
between a flat low-temperature phase and a rough, tensionless, high-temperature
phase. Thus, earlier conclusions on the order of the phase transition and on
the existence of a hexatic phase are seen as due to finite size effects, the
phase diagram of the dLr model being similar to that of a continuum analog
previously formulated in the context of surface growth by MBE.
