Structural and electronic properties of CdS and CdSe clusters

The structural and electronic properties of CdnXn (X=S,Se; n=2–8) are calculated using the finite-difference pseudopotential method in real space. The computed ground state atomic configurations for the CdnXn clusters deviate substantially from those for Si2n and GanAsn. The increased ionic character of the bonding in CdnXn clusters accounts for the observed structural variations. We calculate the highest occupied molecular orbital–lowest unoccupied molecular orbital gaps, binding energies, and polarizabilities of the clusters. We find a strong correlation between the binding energies and gaps. The computed polarizabilities for the (CdS, CdSe) clusters follow the same trend with size as for Si and GaAs. The polarizabilities rapidly approach the bulk limit from above for clusters with more than ∼10 atoms.