Calculated surface and interstitial transition barriers were presented for Ti, O, O2, TiO and TiO2 atoms and clusters at the rutile (110) surface. Defect structures involving these small clusters, including ad-cluster and interstitial binding sites, were calculated by energy minimization using density-functional theory. Transition energies between these defect sites were calculated using the NEB method. Additionally, a modified SMB-Q charge equilibration empirical potential and a fixed-charge empirical potential were used for a comparison of the transition energy barriers. Barriers of 1.2 to 3.5eV were found for all studied small cluster transitions upon the surface except for transitions involving O2. By contrast, the O2 diffusion barriers along the [001] direction upon the surface were only 0.13eV. The charge equilibration model gave mixed agreement with the density-functional theory calculations, with the barriers ranging between 0.8 and 5.8eV.

Surface and Interstitial Transition Barriers in Rutile (110) Surface Growth. Sanville, E.J., Vernon, L.J., Kenny, S.D., Smith, R., Moghaddam, Y., Browne, C., Mulheran, P.: Physical Review B, 2009, 80[23], 235308