Abstract
The bandstructure of the zinc-blende phase of AlN, GaN, InN is calculated employing the exact-exchange (EXX) Kohn-Sham density-functional theory and a pseudopotential plane-wave approach. The cation semicore d electrons are treated both as valence and as core states. The EXX bandgaps of AlN and GaN (obtained with the Ga 3d electrons included as core states) are in excellent agreement with previous EXX results, GW calculations and experiment. Inclusion of the semicore d electrons as valence states leads to a large reduction in the EXX bandgaps of GaN and InN. Contrary to common belief, the removal of the self-interaction, by the EXX approach, does not account for the large disagreement for the position of the semicore d electrons between the LDA results and experiment.
Highlights
The modern computational methods applied to condensed matter systems are based mainly on Kohn-Sham[1] formalism of density-functional theoryKS-DFT
We use the experimental rather than the theoretical lattice constantswhich can be obtained by minimizing the EXX or LDA total energyto allow for a direct comparison with the experimental band gaps and to avoid shifts in the band gaps due to deformation potentials
The exact-exchangeEXX Kohn-Sham densityfunctional theory is used to calculate the electronic structure of the zinc-blendeZBform of AlN, GaN and InN, with and without including the cation semicore states
Summary
The modern computational methods applied to condensed matter systems are based mainly on Kohn-Sham[1] formalism of density-functional theoryKS-DFT. When used in conjunction with both the local-densityLDAand generalized gradient approximationsGGAfor the exchange-correlationXCpotential, the KS-DFT approach provides a very efficient and successful tool to compute the total energy and other related ground state properties. The most serious shortcoming is the so-called band gap problem: the LDA band gaps of semiconductors and insulators are between about 30 to more than 100% smaller than the corresponding experimental values. Another problem is the underestimation of the binding energies of the semicore electrons. The LDA errors for band gaps as well as for binding energies of semicore states have been attributed[5] to a spurious self-interaction in LDA and GGA calculations.[3,6]
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