STRUCTURE OF DISILOXANE - A SEMIEMPIRICAL AND POST-HARTREE-FOCK STUDY

The semiempirical (MNDO, AM1, and PM3) and ab initio predicted structu re of disiloxane is studied with a series of basis sets and inclusion of electron correlation at MP2, MP3, MP4, CCD, CCSD, and CCSD(T) level s. The calculated molecular geometry and barrier to linearization of t he Si-O-Si bond angle are compared with previous theoretical and exper imental values. Our results show that the calculated barrier to linear ization is very sensitive to the number of polarization functions in t he basis set. We also investigate the coupling between the Si-O-Si bon d angle and the Si-O bond length and calculate the Mulliken and electr ostatic potential-derived charges. For comparison purposes we also cal culate the molecular geometry, the barrier to linearization of the Si- O-Si bond angle, and the atomic charges in hexamethyldisiloxane. (C) 1 994 by John Wiley and Sons, Inc.