Ab initio molecular orbital calculations on silica rings

The ab initio molecular orbital 3-21G method was applied to silica rings with two to six tetrahedra per ring. The geometries of the rings and their total electronic energies are compared with previous ab initio, AM1 and PM3 results and with experimental values for amorphous silica. The 3-21G method appears to reproduce with accuracy the experimental results. The semi-empirical PM3 method also gives results that compare favourably with the ab initio calculations and thus is concluded to be suitable for use in calculations on bigger silica clusters. (C) 1999 Elsevier Science B.V. All rights reserved.