We have employed density functional theory to investigate the (110), (101), (100), and (001) surfaces of SnO 2 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. V

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First‐principles calculations and thermodynamics analyses were combined to study the surface stabilities of 3C–SiC and H2O adsorption on the (110) surface. The stoichiometric (110) surface was predicted to be generally the most stable. Only at the extremely C‐poor condition, the nonstoichiometric Si‐terminated (100) could become more energetically favored. The adsorption and dissociation of single H2O molecule on the 3C–SiC (110) were then comparatively investigated. Calculations show that H2O molecules prefer to partially dissociate into one hydroxyl OH and one H adsorbed at the top‐most Si and C sites, respectively, leading to the formation of a hydrogen network on the surface. The calculated equilibrium adsorption diagram further suggested that the 3C–SiC (110) surface can be only either completely clean or fully covered by the partially dissociated species of H2O, for a wide range of temperature and the partial potential of H2O.

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The photophysical properties of Cu-doped CdSe quantum dots (QDs) can be affected by the oxidation state of Cu impurity, but disagreement still exists on the Cu oxidation state (+1 or +2) in these QDs, which is debated and poorly understood for many years. In this work, by using density functional theory (DFT)-based calculations with the Heyd–Scuseria–Ernzerhof (HSE) screened hybrid functional, we clearly demonstrate that the incorporation of Cu dopants into the surface of the magic sized Cd33Se33 QD leads to non-magnetic Cu 3d orbitals distribution and Cu+1 oxidation state, while doping Cu atoms in the core region of QDs can lead to both Cu+1 and Cu+2 oxidation states, depending on the local environment of Cu atoms in the QDs. In addition, it is found that the optical absorption of the Cu-doped Cd33Se33 QD in the visible region is mainly affected by Cu concentration, while the absorption in the infrared regime is closely related to the oxidation state of Cu. The present results enable us to use the doping of Cu impurity in CdSe QDs to achieve special photophysical properties for their applications in high-efficiency photovoltaic devices. The methods used here to resolve the electronic and optical properties of Cu-doped CdSe QDs can be extended to other II-VI semiconductor QDs incorporating transition-metal ions with variable valence.