We investigate the electronic properties of the technologically important wide-band-gap semiconductor GaN employing 'state-of-the-art' DFT-LDA calculations using a FP-LAPW code. The Ga 3d electrons are treated both as core or as valence electrons and the wurtzite as well as the zincblende modifications of GaN are investigated. In particular, we address the influence of the lattice configuration and of the d electrons to the electronic structure of w-GaN and c-GaN. Band structures, densities of states, orbitalresolved densities of states, total and partial valence charge densities, and ionicity factors are analysed in great detail. The calculated values of the energy gaps, bandwidths, spin-orbit, crystal-field splittings, and the correct band degeneracies are compared to experimental and/or ab initio results. Several features of w-GaN resemble those of c-GaN. Most of the calculated band parameters, of band gaps, total and upper-valence bandwidths, and antisymmetric gap for w-GaN are close to those of c-GaN within 1%. The charge distributions have similar features meaning that this material has the same ionicity factor with or without Ga 3d hybridization in both structures. By examining the pressure dependence of the energy band gaps, the value of the hydrostatic deformation potential of the band gap has also been calculated.
The structural, elastic and electronic properties of Ti 2 InC and Ti 2 InN compounds have been calculated using the full-potential linear muffin-tin orbital (FP-LMTO) method. The exchange and correlation potential is treated by the local density approximation (LDA). The calculated ground state properties, including, lattice constants, internal parameters, bulk modulus and the pressure derivative of the bulk modulus are in reasonable agreement with the available data. The effect of pressure, up to 40 GPa, on the lattice constants and the internal parameters is also investigated. Using the total energy-strain technique, we have determined the elastic constants Cij, which have not been measured yet. The band structure and the density of states (DOS) show that both materials have a metallic character and Ti 2 InN is more conducting than Ti 2 InC . The analysis of the site and momentum projected densities shows that the bonding is achieved through a hybridization of Ti -atom d states with C ( N )-atom p states. Otherwise, it has been shown that Ti – C and Ti – N bonds are stronger than Ti – In bonds.
The ground state electronic structure of wurtzite AlN, GaN, and InN has been calculated using fullrelativistic all-electron full-potential linearized-augmented plane-wave method. Several DFT exchangecorrelation functionals, including the recently proposed non-empirical meta-generalised gradient approximation (Meta-GGA) have been used. The role played by relativistic effects and meta-GGA functional on the band structures and the density of states is discussed. We find that the meta-GGA improves the accuracy of the structural properties as well as the energies of the semicore d states in both GaN and InN. This new functional slightly outperforms the local density approximation (LDA) and the generalized gradient approximation (GGA) overall as to lattice parameters, bulk modulus, and valence band widths. We find also that the meta-GGA induced modifications of the band structure are significant, but limited to the valence band states, while leaving all other features identical to LDA and GGA calculations. Finally, our results show that GaN and InN present anomalous dependence of the valence band splitting versus pressure.
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