The site occupancy and elastic modulus of off-stoichiometric Ni 2 MnGa alloys are investigated by the use of the first-principles exact muffin-tin orbital method in combination with coherent-potential approximation. The stable site occupancy at 300 K is determined by comparing the free energies of the alloys with different site-occupation configurations. It is shown that, for most of the off-stoichiometric Ni 2 MnGa, the "normal" site occupation is favorable, i.e., the excess atoms of the rich component occupy the sublattice͑s͒ of the deficient one͑s͒. Nevertheless, for the Ga-rich alloys, the excess Ga atoms have strong tendency to take the Mn sublattice no matter if Mn is deficient or not. Based on the determined site occupancy, the elastic moduli of the off-stoichiometric Ni 2 MnGa are calculated. We find that, in general, the bulk modulus increases with increasing e / a ratio ͑i.e., the number of valence electrons per atom͒. The shear moduli CЈ and C 44 change oppositely with e / a ratio: CЈ decreases but C 44 increases with increasing e / a. However, the Mn-rich Ga-deficient alloys deviate significantly from this general trend. The correlation of calculated elastic moduli and available experimental martensitic transformation temperatures ͑T M ͒ demonstrates that the alloy with larger CЈ than that of the perfect Ni 2 MnGa generally possesses lower T M except for Ni 2 Mn 1+x Ga 1−x .

The electronic structure of the full-and half-Heusler alloys have been studied by ab-initio calculations using full potential augmented plane-wave-method (FLAPW). It was shown that obtained equilibrium lattice parameters and magnetic moments agree well with available experimental data. The influence of vacancies on the electronic structure and magnetic properties of Ni 2Àx MnGa and Co 2Àx ZrSn is analyzed.

Oxygen and fluorine adsorption and their coadsorption on the (111) unreconstructed surface of semiconductors InAs and GaAs were studied using the projector augmented-wave method with the generalized gradient approximation for the exchange−correlation functional and hybrid functional approach. The energetically preferable adsorbate sites on the surface were determined. It is shown that fluorine adsorption above surface cations on the A III B V (111)A-(1 × 1) unreconstructed surface leads to a removal of the surface state formed by cation p z -orbitals and to an unpinning of the Fermi level, whereas oxygen adsorption induces additional surface states in the band gap. The influence of fluorine and oxygen coadsorption and also fluorine concentration on the surface states in the band gap is discussed. It is shown that oxygen-induced surface states are completely or partially removed from the band gap by fluorine coadsorption if it forms bonds with cation surface atoms involved in an interaction with oxygen. The increase of fluorine concentration leads to considerable changes of the near-surface-layer structure due to the penetration of both electronegative adsorbates into the substrate and affects the electron properties of oxygen/ A III B V (111) interface.

EELS L 3,2 ionization edges in several Ni-based intermetallic compounds have been studied and interpreted in terms of the distribution of electrons in the valence d bands. It is demonstrated that the integral EELS cross sections change only slightly upon the formation of intermetallic compounds and, therefore, the charge transfer between atoms is negligible. On the other hand, changes in the energy loss near edge fine structure ͑ELNES͒ of the Ni L 3 edge can be readily detected, indicating an important redistribution of d electrons at the Ni site. Full-potential linearized augmented-plane-wave calculations of the density of states ͑DOS͒ and simulations of the Ni L 3 edge EELS profiles show that these changes correspond to a hybridization between the Ni d band and d bands of the alloying elements. In contrast, structural transformations in the investigated intermetallic compounds do not significantly affect the ELNES as the typical energy resolution of EELS is not sufficient to track the slight difference in the DOS between various structural modifications of intermetallic compounds.