A semiempirical molecular orbital calculation (MOPAC-PM3) was applied to investigate the effects of crystal arrangement, phenyl capping, and dieter formation for CdS nanoparticles. Molecular structures of possible polynuclear cadmium complexes were classified into four categories, zinc blonde (ZB) tetrahedron, ZB cuboctahedron, wurtzite (W), and ZB-W mixture, and the last one is found to be the most favorable formation. The first excitation energies for these cluster complexes were calculated as the HOMO-LUMO energy difference and compared with the absorption peak energy reported in the literature. The electronic effect in polynuclear Cd thiophenolate complexes was discussed in terms of the fractionated density of states as an anti-pi-bond interaction between the benzene pi-orbital and the S 3p-orbitals. The dieter formation did not affect significantly the excited state of the nanoparticle dieter based on the estimation of intramolecular election interaction.