Surface relaxation in CdSe nanocrystals

Total energy minimization is applied to semiempirical tight-binding CdSe nanocrystal models with diameter up to 31 Angstrom. The crystallites have wurtzite lattice structure and ligand-terminated surfaces. It is found that the qualitative features of the surface relaxation in nanocrystals and at bulk surfaces are similar. When surface relaxation is incorporated, the onsets of absorption are determined by interior-to-interior transitions with little contribution from surface-localized states. The fine structure and exchange splittings derived from these clusters are in good agreement with experimental measurements. The effects of ligand parametrization, surface atom composition, and the contribution of surface states to the exciton fine structure are analyzed. (C) 1999 American Institute of Physics. [S0021-9606(99)70320-X].