No abstract

Ab initio calculations based on the density-functional pseudopotential approach have been used to study the fully relaxed structure, the electron distribution and the electronic density of states of (001) terraces, steps, corners and reverse corners, and of F-centers at these surface features on MgO. The calculations confirm earlier predictions of the relaxed structures of surface irregularities based on simple interaction models. A substantial narrowing of the band-gap is found at the surface, which for terraces and steps is due to surface states at the bottom of the conduction band, but for the corner and reverse corner is also due to surface states at the top of the valence band. The F-center formation energy decreases steadily as the coordination of the oxygen site is reduced. The energy of the F-center level shows a tendency to approach the top of the valence band as the coordination of its site decreases.

First-principles calculations based on density functional theory and the pseudopotential method have been used to investigate the influence of gradient corrections to the standard LDA technique on the equilibrium structure and energetics of rutile TiO 2 and SnO 2 perfect crystals and their (110) surfaces.We find that gradient corrections increase the calculated lattice parameters by roughly 3 %, as has been found for other types of material. Gradient corrections give only very minor changes to the equilibrium surface structure, but reduce the surface energies by about 30 %.

First-principles molecular dynamics simulations having a duration of 8 ps have been used to study the static, dynamic and electronic properties of ℓ-Ga at the temperatures 702 K and 982 K. The simulations use the densityfunctional pseudopotential method and the system is maintained on the Born-Oppenheimer surface by conjugate gradients relaxation. The static structure factor and radial distribution function of the simulated system agree very closely with experimental data, but the diffusion coefficient is noticeably lower than measured values. The long simulations allow us to calculate the dynamical structure factor S(q, ω). A sound-wave peak is clearly visible in S(q, ω) at small wavevectors, and we present results for the dispersion curve and hence

No abstract