The electronic and structural properties of molecules (octahydrosilsesquioxane, H8Si8O12), the monosubstituted and higher phenyl-substituted octahydrosilsesquioxanes (PhH7Si8O12, Ph2H6Si8O12, (Ph-Ph)H7Si8O12, and Ph8Si8O12), and crystals (H8Si8O12 and octa(phenylsilsesquioxane) acetone solvate (C48H4O12Si8.C3H6O)) have been studied using plane-wave (PW), pseudo-potential (PP), and density functional theory and the generalized gradient approximation (DFT-GGA) methods. The results show that the orbitals near the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) (inclusive) for the phenyl-substituted polyhedral oligomeric silsesquioxane clusters and crystal are localized on the phenyl functional groups, whereas for both isolated molecular and crystalline H8Si8O12, the HOMO is that with the lone pair on the O atoms.