ATOMIC-STRUCTURE OF THE SI(100)-(2X1) SURFACE

Abstract

We have studied the atomic structure of the Si(100)-(2 X 1) surface by carrying out the pseudopotential density-functional total-energy calculations. The Si atoms in the top-three surface layers are relaxed along the calculated Hellmann-Feynman atomic forces in an 8-layer thin-film supercell geometry. Within a symmetric-dimer reconstruction model, the equilibrium top-layer dimer length is 2.20 angstrom and the nearest-neighbor bond length between the top- and second-layer Si atoms is 2.29 angstrom, which are in good agreement with the previous pseudopotential studies. From independent calculations using a simple top-layer-relaxation model, we find that these surface bond lengths are changed little by multilayer relaxation and also that the symmetric-dimer surface structure is stable over a wide range of asymmetric distortions of the dimer along the surface normal direction, i.e., there is no local energy minimum in asymmetric dimer distortion.