ELECTRONIC AND STRUCTURAL-PROPERTIES OF GAN BY THE FULL-POTENTIAL LINEAR MUFFIN-TIN ORBITALS METHOD - THE ROLE OF THE D-ELECTRONS

The structural and electronic properties of cubic GaN are studied with in 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. Due to the energy resonance of Ga 3d states with nitrogen 2s states, the cation d bands are not inert, a nd features unusual for a III-V compound are found in the lower part o f the valence band and in the valence charge density and density of st ates. To clarify the influence of the d states on the cohesive propert ies, additional full- and frozen-overlapped-core calculations were per formed for GaN, cubic ZnS, GaAs, and Si. The results show, in addition to the known importance of core-valence exchange-correlation nonlinea rity, that an explicit description of closed-shell interaction has a n oticeable effect on the cohesive properties of GaN. Since its band str ucture and cohesive properties are sensitive to a proper treatment of the cation d bands, GaN appears to be somewhat exceptional among the I II-V compounds and reminiscent of II-VI materials.