O2 diffusion in SiO2: triplet versus singlet

We address the diffusion of the oxygen molecule in SiO2, using first-principles spin-polarized total-energy calculations. We find that the potential energy surfaces for the singlet and triplet states are very different in certain regions, and that the O2 molecule preserves its spin-triplet ground state not only at its most stable interstitial position inside the solid but also throughout its diffusion pathway. Therefore, the singlet state is not a good approximation to describe the behavior of O2 inside SiO2, and spin-polarization effects are fundamental to understand the properties of this system.