AN AB-INITIO INVESTIGATION OF THE LOWEST POTENTIAL-ENERGY SURFACE OF DISILOXANE

In a recent study, Nicholas and co-workers used extended basis sets and electron correlation to examine disiloxane. They studied two C2v structures and an intermediate structure with an Si-O-Si bond angle of 180-degrees. This study continues the previous work and examines more of the potential energy surface. In particular, the potential surface is examined by fixing two H-Si-O-Si dihedral angles and allowing all other internal coordinates to optimize. Each optimization is performed at the Hartree-Fock level with the 6-31G(D) basis set (HF/6-31G(D)) and using second order Moller-Plesset perturbation theory with both the 6-31G(D) and 6-311G(D,P) basis sets (MP2/6-31G(D) and MP2/6-311G(D,P), respectively). An examination of each surface shows that a C(s) gully is present that connects the two C2v structures, one being the minimum and the other being close to a transition structure. The variation of selected internuclear bond lengths and angles along this C(s) path is presented as well as for the ''linear'' structure using optimizations at these three levels of theory as well as at the MP2/6-311G(2D,P) level. The effects of these computational results on the possible form of an empirical potential to model zeolites and clays is also discussed.