We have studied the stability, the electronic, and the magnetic properties of Co2MnSi(001) thin films for 15 different terminations using density functional theory calculations. The phase diagram obtained by ab initio atomistic thermodynamics shows that in practice the MnSi, pure Mn, or pure Si terminated surfaces can be stabilized under suitable conditions. Analyzing the surface band structure, we find that the pure Mn termination, due to its strong surface-subsurface coupling, preserves the half-metallicity of the system, while surface states appear for the other terminations.

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The ab initio full potential linearized augmented plane wave (FP-LAPW) method within density functional theory was applied to study the effect of composition on the structural and electronic properties of Zn 1-x Be x S, Zn 1-x Be x Se and Zn 1-x Be x Te ternary alloys. The effect of composition on lattice parameter, bulk modulus, band gap and effective mass was investigated. Deviations of the lattice constant from Vegard's law and the bulk modulus from linear concentration dependence were observed for all three alloys. It was deduced that increasing the Be composition in the alloys increases the hardness of the materials. In addition, the calculated band structures showed that the band gap undergoes a direct-to-indirect transition at a given concentration. Using the approach of Zunger and co-workers, the microscopic origins of band gap bowing have been explained. The electron (hole) effective masses were also calculated. The band gap and effective mass were found to vary non-linearly with Be composition.

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Zn 1−x Mg x S, Zn 1−x Mg x Se and Zn 1−x Mg x Te ternary wide-gap semiconductor alloys were investigated using the full potential-linearized augmented plane wave (FP-LAPW) method. We have studied the effect of composition on structural properties such as lattice constants, bulk modulus and bond ionicity. The bandgap and the microscopic origins of compositional disorder have also been explained in detail. In addition, from the obtained band structures, the electron (hole) conduction and valence effective masses are deduced. These parameters were found to depend non-linearly on alloy composition x, except the lattice parameter for Zn 1−x Mg x S, which follows Vegard's law. The calculated band structures for all three alloys show a direct bandgap in the whole range of x composition. We have paid special attention to the disorder parameter (gap bowing). Using the approach of Zunger and co-workers, we have concluded that the total bandgap energy bowing was mainly caused by the charge exchange effect for the alloys of interest.

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