Ab initio tight-binding analysis of CdS nanocrystals

Spherical CdnSm nanocrystals are studied via an ab Initio tight-binding analysis. Starting from the bulk zinc-blende structure, these nanocrystals undergo relaxation as the geometries optimize to configurations that minimize internal forces. The resulting electronic structure and molecular orbitals are analyzed and compared to the electronic structure and molecular orbitals found in the bulklike zinc-blende structure. We conclude that the states found in the gap between the valence band and the conduction band are mainly on the surface of the nanocrystals and are due to the unpassivated bonds that remain after surface relaxation.