To understand ligand capping effects on the structure and electronic properties of Cd n X n (X=Se, Te; n=3, 4, 6, and 9) species, we performed density functional theory studies of SCH 2 COOH–, SCH 2 CH 2 CO 2 H–, and SCH 2 CH 2 NH 2 –capped nanoparticles. Cd n X n capping with all three capping groups was found to produce significant NP distortions. All three ligands destabilize the NP HOMOs and either stabilize or destabilize their LUMOs, leading to closure of the HOMO/LUMO gaps for all of the capped species, because the HOMO destabilization effect is generally large than the LUMO destabilization effect. The calculated absorption spectra of bare and capped NPs, exemplified by Cd n X n with n=4 and 6, show that all capping groups cause noticeable red shifts for n=4 and mostly blue shifts for n=6.