A ug 1 99 2 Electronic and structural properties of GaN by the full - potential LMTO method : the role of the d electrons

The structural and electronic properties of cubic GaN are studied within the local density approximation by the full-potential linear muffin-tin orbitals method. The Ga 3d electrons are treated as band states, and no shape approximation is made to the potential and charge density. The influence of d electrons on the band structure, charge density, and bonding properties is analyzed. It is found that due to the energy resonance of the Ga 3d states with nitrogen 2s states, the cation d bands are not inert, and features unusual for a III-V compound are found in the lower part of the valence band and in the valence charge density and density of states. To clarify the influence of the Ga d states on the cohesive properties, additional full and frozen–overlapped-core calculations were performed for GaN, cubic ZnS, GaAs, and Si. The results show, in addition to the known importance of non-linear corevalence exchange-correlation corrections, that an explicit description of closed-shell repulsion effects is necessary to obtain accurate results for GaN and similar systems. In summary, GaN appears to be somewhat exceptional among the III-V compounds and reminiscent of II-VI materials, in that its band structure and cohesive properties are sensitive to a proper treatment of the cation d bands, as a result of the presence of the latter in the valence band range.