Bound hole states induced by excess oxygen in La 2 CuO 4+ are studied in the framework of the extended Hubbard model, using the spin-wave approximation and the Lanczos algorithm. We interpret the band at 0:5 eV in the impurity reeectivity spectrum as connected with the transition from the lowest bound hole level (S z = 1=2) to the unperturbed hole band. It is shown that in the realistic paramet...

Raman scattering experiments from high-1; superconductors of the RBa2Cu307-~ type, with R Y, Pr, Nd, Eu, Gd, Dy, and Yb, are reported. Because of the great difBculty in obtaining single-phase samples, spectra from all starting compounds and other known phases of Y-Ba-Cu are presented. This systematic approach has allowed the identi6cation of the lines observed in Raman spectra of the supercondu...

The transition from shallow to deep centers as a function of pressure or alloying is investigated for oxygen and silicon donors in GaN and AlN, based on first-principles total-energy calculations. The stability of the localized deep state (DX center! is found to depend on interactions between the impurity and third-nearestneighbor atoms, which occur in different positions in the zinc-blende and...

We report a comprehensive theoretical study of structural and electronic properties of substitutional oxygen and zinc contaminations in a model of single wall GaN nanotubes by means of ab initio supercell calculations. Our investigation yields many interesting results. The following ones deserve to be developed. Oxygen forms a shallow donor in the single wall GaN nanotubes as in bulk GaN polyty...

Water adsorption and dissociation on the perfect, oxygen containing and nitrogen vacancy containing Ta3N5(100) surfaces are systematically studied by density functional theory calculations. The results show that the perfect Ta3N5(100) surface is very active for water dissociation because of the dangling bonds formed on the perfect Ta3N5(100) surface. The presence of oxygen on the surface is abl...

We investigate the behavior of impurity fields immersed in a larger condensate field in various dimensions. We discuss the localization of a single impurity field within a condensate and note the effects of surface energy. We derive the functional form of the attractive condensate-mediated interaction between two impurities. Generalizing the analysis to N impurity fields, we show that within va...

30 Si(n,ƒÁ)31Si2.62h +31P+ƒÀ(1) Irradiated silicon crystals are heavily damaged and electrical resistivity changes drastically. The lattice damage can be removed by an appropriate annealing. The change in resistivity of the silicon crystals is quite complex. It depends on both impurity atoms contained originally in silicon and atoms produced by nuclear reactions. This note describes the determi...

From the basis of ab initio electronic structure calculations which include the effects of thermally excited magnetic fluctuations, we predict Mn-stabilized cubic zirconia to be ferromagnetic above 500 K. We find this material, which is well known both as an imitation diamond and as a catalyst, to be half-metallic with the majority and minority spin Mn impurity states lying in zirconia's wide g...

Titanium dioxide, TiO 2 , is a widely used, yet quite inefficient photocatalyst. Among the important drawbacks, its band gap is rather large for efficient use of sunlight, and control of trapping and recombination sites for photo-excited carriers is very limited. In this talk I will present results of theoretical studies aimed at obtaining insights into issues relevant to TiO 2-based photocatal...

The metal-insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here we combine X-ray absorption and resonant inelastic X-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of...