Electronic structure of substitutional defects and vacancies in GaSe

We have investigated the nature of defect states associated with substitutional impurities (Cd, In, Sn) and both Ga and Se vacancies in GaSe using ab initio electronic structure methods within density functional theory. These calculations were done using supercell model allowing for internal atomic relaxation. Binding energies (BEs) of defects obtained in this model are compared with effective mass approximation results. Significant central cell corrections are present for most of the defects. This is consistent with charge densities associated with the defect states that show clearly their strongly localized nature. Because of the difficulties associated with LDA/GGA in giving the correct band gap in semiconductors, we have only compared the acceptor BEs with available experiments. Our theoretical results agree well with the experiment for Cd_Ga and V_Ga. The fundamental role played by the Ga dimers in the formation of defect states is discussed.     

Theoretical study of encapsulated alkali metal atoms in nanoporous channels of ITQ-4 zeolite: one-dimensional metals and inorganic electrides

Electronic structure calculations within density-functional theory have been carried out in a class of novel inorganic electrides M-ITQ-4 zeolite (M = Na, K, Rb, Cs) to understand the competing effects of guest-guest (M-M) and guest-host (M-ITQ-4) interactions. We find that Na forms a nearly perfect 1D metal undergoing Peierls distortion whereas Cs couples rather strongly to the host accompanied by a large charge transfer. In addition to the guest-host high energy charge transfer excitations we find a new far infrared excitation peak in Na at approximately 0.35 eV that can be ascribed to the Peierls distortion.     

Non-Stoner continuum in the double exchange model

Exact diagonalization studies of the double exchange model indicate the existence of continuum states in the single-spin-flip channel that overlap the magnons at very low energies (approximately 10(-2) eV) and extend to high energies (approximately eV). This picture differs dramatically from the prevalent view, where there are the magnons, plus the Stoner continuum at the high-energy scale, with nothing in between. The relevance of these new continuum states to inelastic neutron scattering and optical properties is discussed.     

Theory of electronic structure and nuclear quadrupole interactions in the BF3–NH3 complex and methyl derivatives

Magnetic Hyperfine and Nuclear Quadrupole Interactions (HFI and NQI) are now important tools for characterization of systems of interest in materials research and industry. Boron-Trifluoride is an inorganic compound that is very important in this respect as a catalyst in chemical physics research and industry, forming complexes in the process with compounds like ammonia, water and methyl alcohol. The present paper deals with the BF₃–NH₃ complex and methyl derivatives BF₃NH_x(CH₃)_3?x for which we have studied the electronic structures, binding energies, and ¹⁹F* (I?=?5/2) nuclear quadrupole interactions using the first-principles Hartree–Fock–Roothaan procedure combined with electron correlation effects. Our results for the ¹⁹F* nuclear quadrupole coupling constant (e ² qQ/h) in units of MHz compare well with experiment. Trends in the binding energies and NQI parameters between the complexes are discussed.