Spreading of step-like density profiles in interacting lattice gas on a hexagonal lattice

Diffusion in a single-layer adsorbate on a crystalline surface with a hexag onal lattice site symmetry is studied by Monte Carlo simulations. A step-li ke density profile of the adsorbate is allowed to spread. From the evolutio n of this density profile the diffusion coefficient is obtained by use of s tandard Boltzmann-Matano analysis. Results are compared with those obtained from the harmonic profile evolution studies undertaken by us previously. A greement between both approaches is found at high and low temperatures. We show results for systems with two different activated state energies. For t he first model the diffusion coefficient increases smoothly with the densit y, and for the second one the diffusion coefficient reaches a maximum for a half-occupied lattice. For this density the step profile forms a long flat terrace. No increase of the diffusion constant for densities where perfect ordering happens was observed. (C) 2000 Published by Elsevier Science B.V. All rights reserved.