Structure of amorphous TeO2 revisited: A hybrid functional ab initio molecular dynamics study

Abstract

The atomic-scale structure of glassy ${\mathrm{TeO}}_{2}$ has been the subject of a longstanding debate. We resort to first-principles molecular dynamics with a careful choice of the exchange and correlation functional to achieve a good agreement with experimental findings for the topology of glassy and molten ${\mathrm{TeO}}_{2}$. We show that only molecular dynamics at the hybrid functional level of theory is able to reproduce a correct description of the medium-range order in the glass. Based on a Wannier-function decomposition of the electronic structure, we show that the coordination number of tellurium is around 4 and that there is a non-negligible fraction of nonbridging oxygen atoms. An analysis of the net atomic charge distribution shows that an increase of the Te-O-Te bridge asymmetry strongly correlates with the charge on the oxygen atom. Additionally, we find that the oxygen bridge asymmetry increases with temperature, which strengthens the short-range disorder in molten ${\mathrm{TeO}}_{2}$, and consequently lowers the coordination number of Te. These results provide a revisited picture of the ${\mathrm{TeO}}_{2}$ network connectivity and its evolution as a function of temperature.