USE OF EFFECTIVE CORE POTENTIALS FOR ABINITIO CALCULATIONS ON MOLECULAR SILOXANES AND SILICATES

A series of ab initio electronic structure calculations have been performed on the (H3Si)2O molecule using a range of basis sets. The accuracy of these calculations was evaluated by comparison with several experimental measurements. These calculations support earlier results indicating that polarization functions on the bridging oxygen atom are usually required to obtain a bent geometry for the Si-O-Si linkage in disiloxane. It was found that ab initio calculations utilizing effective core potentials and a double-zeta valence description augmented with polarization functions (CEP-31G*) provide results comparable in quality to those obtained using the all-electron 6-31G* basis set. To demonstrate the general utility of these effective core potential basis sets for theoretical studies of molecular silicates, calculations were performed on the (HO)3SiOSi(OH)3 molecule. The results obtained are in excellent agreement with previous experimental and ab initio calculations using all-electron basis sets.