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.