Using a molecular dynamics DFT-LDA code, we have analyzed the Schottky-barrier formation of a Se-passivated GaAs(1 0 0)-2 x 1 reconstruction. In our approach we consider, first, the energetically most favorable interfaces formed by the deposition of either one or two Ga atoms per surface unit cell; then, we analyze the electron density of states and calculate the interface Fermi level and the Schottky-barrier height. We show that the height depends essentially on the very same interface geometry. In particular, the effect of exchanging Ga and Se atoms at the interface (an intermixing process) yields a normal Schottky-barrier height, while the normal passivated surface yields an ohmic contact. (C) 2002 Elsevier Science B.V. All rights reserved.