Structure and properties of disiloxane: An ab initio and post-hartree-fock study

As a prototype of the Si - O - Si bonding region for silica modeling, especially the highly flexible Si - O - Si angle deformation, we studied the structure of disiloxane (H₃Si - O - SiH₃), with ab initio calculations on the SCF, MBPT (2), CCSD, and CCSD(T) levels of theory. The convergence of the results is studied for a series of basis sets of increasing quality. Large basis sets including f functions are necessary to obtain reliable results for the structure and the barrier to linearization of the molecule. The following structure and energy parameters are the results of CCSD(T)-fc/cc-pVTZ calculations: Si - O distance is 1.645Å, the Si - O - Si angle 145.3° and the barrier to linearization 0.48 kcal/mol.