H6SI2O7 - ABINITIO MOLECULAR-ORBITAL CALCULATIONS SHOW 2 GEOMETRIC CONFORMATIONS

The canonical H6Si2O7 molecule has been used over the last twenty years to characterize by molecular orbital calculations properties of the Si-O bond in silica containing aqueous solutions, crystalline, or amorphous silicates. The fact that constrained calculations reproduced all essential properties within the accuracy of experimental observations inspired us to optimize without any constraints the energy and geometry of such molecule by means of ab initio molecular orbital calculations, and to match the calculated properties of the true geometry of H6Si2O7 with properties for silica materials. Our ab initio calculations reveal the following features: a local total energy minimum at < Si-O-Si of 135-degrees and a slightly lower minimum at 123-degrees, associated with one and two hydrogen-oxygen bridges.