Quantum chemical simulation of cadmium chalcogenide clusters

Under diminishing size of semiconductor nanoparticles (quantum dots) they change properties dramatically due to familiar quantum size effects. The species of the lowest possible size corresponding semiconductor crystal lattices (clusters) possess the maximum quantum confined features. They are of interest to follow the transition between molecular properties of few-atomic precursors and nuclei of a solid phase. We consider quantum chemical modeling of cadmium chalcogenide clusters containing tens of atoms. They may be the fragments of bulk lattices and nave arbitrary geometries. Ab initio geometry optimization (at the restricted Hartree-Fock level) together with electronic structure analysis allows to find possible structures of the CdnXm-clusters (X=S,Se,Te) terminating with hydrogen atoms. The clusters considered (up to n=17, m=32) reveal the dramatic variation of properties with size, interband gap is much higher than for the bulk counterparts for all chalcogenides, and simulate well some experimental findings on spectral properties of (CdX)(n) produced in colloids with organic ligand capping. The results obtained are important as a theoretical base of small semiconductor clusters those do not described within the effective mass approximation and as pathways to discover a growth sequence of these species towards bigger nanoparticles.