DENSITY-FUNCTIONAL STUDY OF THE EQUILIBRIUM GEOMETRY AND SI-O-SI POTENTIAL-ENERGY CURVE OF DISILOXANE

Calculations of the barrier to linearization of disiloxane using vario us methods (HF, MP2, CCSD (T) and DFT) with double-zeta and triple-zet a basis sets plus a single d-set yield very low or no barrier. The CCS D(T) results calculated with triple-zeta basis sets plus a single d-se t is in agreement with recent experimental results (0.30 kcal/mol). Ho wever, the same methods produce a higher barrier ( approximate to 1.4 kcal/mol) using a more expanded basis set. The results calculated with various density functional methods show a similar basis set dependenc e. The inclusion of the f functions into the basis lowers the barrier. The barrier calculated using the combination of Becke and Perdew (B-P 86) functionals is in good agreement with coupled cluster results. The coefficients of a polynomial interpolation for the correlation energy as a function of the Si-O-Si bond angle are also given.