Crystalline lattice effects on tensionless surface dynamics

9 pages, 5 figures.A new model is introduced for two-dimensional crystalline interfaces with negligible surface tension. The model is given by a discrete version of the linear molecular beam epitaxy (MBE) equation plus an additional term periodic in the interface height variable. Langevin dynamics simulations and analytical arguments show that the model exhibits a roughening transition to the high temperature phase of the sine-Gordon model, whose initial stages are nevertheless described by the scaling of the linear MBE equation. Out of equilibrium, the model can have three different behaviors depending on temperature and deviation from equilibrium: A non-moving flat interface, a moving interface with oscillatory roughness, and a moving interface which shows scaling. Possible connections to experiments are discussed.This work has been supported by CICyT (Spain) grant MAT95-0325.Publicad