Environment-dependent surface structures and stabilities of SnO2 from the first principles

We have employed density functional theory to investigate the (110), (101), (100), and (001) surfaces of SnO2 within the pseudopotential, plane-wave method. Based on a thermodynamic defect model, the surface stabilities were evaluated as functions of oxygen partial pressure and temperature. Calculations showed that, below 600 K, the stoichiometric (110) has the lowest surface energy for a wide range of oxygen partial pressures, followed by the (100), (101), and (001). At higher temperatures, the stability transition from the stoichiometric to a Sn-rich termination tends to occur on all these surfaces (except the (001)) at ultrahigh vacuum. Such transitions may shift to higher pressures with increasing temperature. An equilibrium surface phase diagram was then developed to illustrate the environment dependence of these surfaces. The electronic structure of the stoichiometric (110) was also analyzed based on the electron density of states and differential charge density distribution.