A. Antons, R. Berger, S. Blügel and K. Schroeder

We have simulated STM images for the most stable structures of (112) and (112) oriented steps on As terminated Si(111) using the TersofF Hamann-aproximation. The structures are determined using first-principles molecular statics calculations based on total energy and force minimization. All calculations are carried out with our EStCoMPP-code within the density functional formalism in the local-density approximation, using norm-conserving separable pseudopotentials and a planewave basis-set. On Si(111):As the steps always have the height of a double layer. For both step orientations the exposed second layer Si-atoms at the step edge are replaced by As atoms (As passivated steps). At the (112) step edge this leads to the formation of As dimers. The different structures show up prominently for negative bias voltage when the occupied states are imaged. For positive bias voltage, i. e. in the unoccupied states, differences are washed out to a large extent.