Ab initiostudy of the polymer molecules(TeO2)nas model systems for the local structure inTeO2glass

The equilibrium geometry and energy of formation of the polymer molecules $({\mathrm{TeO}}_{2}{)}_{n}$ with $n=2\char21{}6$ were studied within the ab initio B3LYP method. For each n greater than 2, several stable conformers were found. They are classified into four homologue series: the cyclic molecules built up of corner-sharing ${\mathrm{TeO}}_{3}$ pyramids, chain molecules built up of edge-sharing ${\mathrm{TeO}}_{4}$ units, cyclic molecules built up of edge-sharing ${\mathrm{TeO}}_{4}$ units, and three-dimensional framework structures built up predominantly of corner-sharing ${\mathrm{TeO}}_{4}$ units. The latter structures were shown to possess the lowest energy of formation whose limit at $\stackrel{\ensuremath{\rightarrow}}{n}\ensuremath{\infty}$ was found to agree well with the experimental value of the cohesive energy in paratellurite. These molecules could be representative of the local structures in ${\mathrm{TeO}}_{2}$ glass.