AB-INITIO DENSITY-FUNCTIONAL CALCULATIONS FOR SI(001) BI(1ML)-(2X1)/

We present calculations for atomic geometry, electronic states and bon ding for a monolayer (1 ML) of Bi on the Si(001) surface using a first -principles pseudopotential method. The (2 x 1) surface reconstruction is due to formation of symmetric Bi dimers of length 3.06 Angstrom at a height of 1.76 Angstrom above the Si substrate. This geometry is co mpared with that obtained recently for Si(001)/Sb(1 ML)-(2 x 1). Our r esults show the surface to be semiconducting with covalent bonding bet ween the adatoms and substrate. (C) 1998 Elsevier Science B.V. All rig hts reserved.