Occupation matrix control of d- and f-electron localisations using DFT + U

TiO2 Band Restructuring by B and P Dopants

An examination of the effect of B- and P-doping and codoping on the electronic structure of anatase TiO2 by performing density functional theory calculations revealed the following: (i) B- or P-doping effects are similar to atomic undercoordination effects on local bond relaxation and core electron entrapment; (ii) the locally entrapped charge adds impurity levels within the band gap that could enhance the utilization of TiO2 to absorb visible light and prolong the carrier lifetime; (iii) the core electron entrapment polarizes nonbonding electrons in the upper edges of the valence and conduction bands, which reduces not only the work function but also the band gap; and (iv) work function reduction enhances the reactivity of the carriers and band gap reduction promotes visible-light absorption. These observations may shed light on effective catalyst design and synthesis.

Clustering of Oxygen Vacancies at CeO2(111): Critical Role of Hydroxyls

By performing density functional theory calculations corrected by an on site Coulomb interaction, we find that the defects at the CeO_{2}(111) surface observed by the scanning tunneling microscopy (STM) measurements of Esch et al. [Science 309, 752 (2005)] are not mere oxygen vacancies or fluorine impurities as suggested by Kullgren et al. [Phys. Rev. Lett. 112, 156102 (2014)], but actually the hydroxyl-vacancy combined species. Specifically, we show that hydroxyls play a critical role in the formation and propagation of oxygen vacancy clusters (VCs). In the presence of neighboring hydroxyls, the thermodynamically unstable VCs can be significantly stabilized, and the behaviors of oxygen vacancies become largely consistent with the STM observations. In addition to the clarification of the long term controversy on the surface defect structures of CeO_{2}(111), the "hydroxyl-vacancy model" proposed in this work emphasizes the coexistence of hydroxyls and oxygen vacancies, especially VCs, which is important for understanding the catalytic and other physicochemical properties of reducible metal oxides.

Ni on the CeO2(110) and (100) surfaces: adsorption vs. substitution effects on the electronic and geometric structures and oxygen vacancies

We report density functional theory (DFT) calculations of the interactions of both Ni adsorbate and substitutional dopant with the ceria (110) and (100) surfaces to explain the origin of the activity of Ni/ceria catalysts.

Theoretical study of the structures and chemical ordering of cobalt–palladium nanoclusters

Global optimization of 1 : 1 compositions of (Co–Pd)_N/2 up to N = 150 and all compositions of 34- and 38-atom binary clusters has been performed using a genetic algorithm, coupled with the Gupta empirical potential to model interatomic interactions.

Near Surface Stoichiometry in UO2: A Density Functional Theory Study

The mechanisms of oxygen stoichiometry variation in UO2at different temperature and oxygen partial pressure are important for understanding the dynamics of microstructure in these crystals. However, very limited experimental studies have been performed to understand the atomic structure of UO2near surface and defect effects of near surface on stoichiometry in which the system can exchange atoms with the external reservoir. In this study, the near (110) surface relaxation and stoichiometry in UO2have been studied with density functional theory (DFT) calculations. On the basis of the point-defect model (PDM), a general expression for the near surface stoichiometric variation is derived by using DFT total-energy calculations and atomistic thermodynamics, in an attempt to pin down the mechanisms of oxygen exchange between the gas environment and defected UO2. By using the derived expression, it is observed that, under poor oxygen conditions, the stoichiometry of near surface is switched from hyperstoichiometric at 300 K with a depth around 3 nm to near-stoichiometric at 1000 K and hypostoichiometric at 2000 K. Furthermore, at very poor oxygen concentrations and high temperatures, our results also suggest that the bulk of the UO2prefers to be hypostoichiometric, although the surface is near-stoichiometric.