Computational Study of Magic-Size CdSe Clusters with Complementary Passivation by Carboxylic and Amine Ligands

The
electronic and optical properties of tetrahedral CdSe magic
clusters (average diameter ∼1.5 nm) protected by carboxyl and
amine ligands, which correspond to previously reported experimental
structures, are studied using density functional theory. We find extreme
ligand packing densities, capping every single dangling bond of the
inorganic core, strong dependence of the Z-type metal carboxylate
binding on the amount of excess amine, and potential for improved
photoluminescence upon replacing phenyl ligands with alkanes. The
computed absorption spectra of the Cd35Se20 cluster
agree well with experiments, resolving the 0.2 eV splitting of the
first exciton peak due to spin–orbit coupling. We discuss the
origin of the significant broadening of the optical spectra as due
to phonons and structural variations in the ligand configurations
and inorganic core apexes.