PREROUGHENING, AND DISORDERED FLAT PHASE-SEPARATION IN SURFACE MOLECULAR-DYNAMICS SIMULATIONS

Ordinary molecular dynamics surface simulations are particle-conservin g. We have found that, while this restriction may be adequate for a ma jority of situations, there exists for most surfaces a range of temper atures where that is not the case. The critical temperature range is b etween preroughening and roughening. There, the surface equilibrium st ate is disordered and fiat (DOF), implying a state of roughly half-fil ling for the outermost surface layer. A particle-conserving simulation , based initially on a well-defined, usually integer, number of crysta lline layers, must phase-separate into two half-layered domains. We di scuss evidence, indicating that this kind of phase separation is actua lly taking place in existing simulations.