Effect of cation configuration and solvation on the band positions of zinc ferrite (100).

Zinc ferrite ZnFe[Formula: see text]O[Formula: see text] belongs to the spinel-type ferrites that have been proposed as photocatalysts for water splitting. The electronic band gap and the band edge positions are of utmost importance for the efficiency of the photocatalytic processes. We, therefore, calculated the absolute band energies of the most stable surface of ZnFe[Formula: see text]O[Formula: see text], the Zn-terminated (100) surface at self-consistent hybrid density functional theory level. The effect of Fe- and Zn-rich environments, cation exchange as antisite defects and implicit solvation on the band positions is investigated. Calculated flat band potentials of the pristine surface model ranges from [Formula: see text] to [Formula: see text] V against SHE in vacuum. For Zn-rich (Fe-rich) models this changes 0.3-0.9 (0.0-0.7) V against SHE. Fe-rich models are closest to the experimental range of reported flat band potentials. Solvent effects lower the calculated flat band potentials by up to 1.8 eV. The calculated band gaps range from 1.5 to 2.9 eV in agreement with previous theoretical work and experiment. Overall, our calculations confirm the experimentally observed low activity of ZnFe[Formula: see text]O[Formula: see text] and its dependence on preparation conditions.

Bridging experiment and theory: enhancing the electrical conductivities of soft-templated niobium-doped mesoporous titania films.

Theoretical calculations suggest a strong dependence of electrical conductivity and doping concentration in transition-metal doped titania. Herein, we present a combined theoretical and experimental approach for the prediction of relative phase stability and electrical conductivity in niobium-doped titania as model system. Our method paves the way towards the development of materials with improved electrical properties.

Influence of Spin State and Cation Distribution on Stability and Electronic Properties of Ternary Transition-Metal Oxides.

This work is a systematic ab initio study of the influence of spin state and cation distribution on the stability, dielectric constant, electronic band gap, and density of states of ternary transition-metal oxides. As an example, the chemical family of spinel ferrites MFe2O4, with M = Mg, Sc-Zn is chosen. Dielectric constant and band gap are calculated for various spin states and cation configurations via dielectric-dependent self-consistent hybrid functionals and compared to available experimental data. When choosing the most stable spin state and cation configuration, the calculated electronic properties are in reasonable agreement with measured values. The nature of the excitation is investigated through projected density of states. A pronounced dependence of band gap energy and dielectric constant on the spin state and cation configuration is observed, which is a possible explanation for the large variation of the experimental results, in particular, if several states are energetically close.