SCF AND CORRELATED LEVEL DETERMINATION OF THE MOLECULAR AND VIBRATIONAL STRUCTURE OF ORTHOSILICIC ACID, SI(OH)4

The focus of this investigation was to determine the relevance of electron correlation corrections in predicting the geometry and molecular spectra of model compounds for silicate materials. We have performed a series of ab initio molecular orbital calculations on various isomers of Si (OH)4 at the self-consistent field (SCF) and second-order many-body perturbation theory (MBPT(2)) levels using double-zeta polarized (DZP) quality basis sets. Electron correlation affects both the molecular and vibrational structure of these compounds. The use of a single scaling factor to account for electron correlation and anharmonic effects does not lead to consistent prediction of MBPT(2) properties.