A Diffusion Monte Carlo Study

Self-diffusion of Ti interstitials is essential for TiO₂ photo-catalysts, because it works for maintaining the surface stoichometry and keeping the photo-reactivity. We revisited ab initio evaluations of the barrier energies along the possible diffusion paths of Ti interstitials in rutile TiO₂ bulk using diffusion Monte Carlo method. Our calculation predicted that Ti interstitials diffuse faster in parallel to c-axis, reasonably explaining why rutile TiO₂ has a superior photo-activity on (001) surface to (110). Our prediction does not support the previous GGA-DFT works, and this discrepancy can be explained by the poor cancellation of the self-interactions in GGA-DFT.