Anatase and rutile surfaces with adsorbates representative of acidic and basic conditions

Presented here are density functional theory results of the structure and energetics of selected low index stoichiometric surfaces of the anatase and rutile titanium dioxide polymorphs, passivated with complete monolayers of adsorbates chosen to represent acidic and basic conditions. The adsorbates differ in each case by varying the hydrogen to oxygen ratio with respect to a neutral, water-terminated surface. The results are compared for each of the 30 surfaces examined here, to identify relationships between surface chemistry, surface free energy, surface stress and (upper-most) surface tri-layer reconstructions. Within our model, the results show that termination with water consistently results in the lowest values of surface free energy, but not necessarily the lowest surface stress.