Effect of basis set and of electronic correlation on ab initio calculations on silica rings

The effect of the choice of basis set and of electronic correlation on ab initio calculations on silica rings have been investigated. Silica rings with size varying between 2 and 6 have been modeled with respect to geometry and energetics. It appears from these results that the 6-31G* basis set is required in order to obtain precis results and that any further improvement of this set is not necessary. Electronic correlation contribution has been estimated thank to DFT calculations. It is concluded that this contribution is very important and cannot be neglected. These two main results build the basis for further modeling of silica based systems including the study of the densification of silica gels.