Screened-exchange LDA methods for films and superlattices with applications to the Si(100)2X1 surface and InAs/InSb superlattices

We have developed efficient screened-exchange local-density approximation (sX-LDA) methods for films and superlattices (FLM/SL) with which to calculate self-consistent electronic structures for both occupied and unoccupied states. Considering nonuniform charge densities and local-field effects in the z direction for FLM/ SL, we have employed nonlocal Thomas-Fermi wave vectors to define the screened-exchange interaction. Three methods, for bulk, superlative, and film, have been implemented in the full-potential linearized augmented plane wave method. The film sX-LDA method was then applied to the Si(100)2X1 surface. The calculated occupied surface states show very good agreement with experiment. On the other hand, an underestimation of the correction to the unoccupied surface states, by about 0.2 eV, was estimated in comparison with available GW calculations. The ionization energy of Si was evaluated with the film geometry to be 5.35 eV by virtue of the quasiparticle corrections, showing good agreement with the experimental value of 5.15 ±0.08 eV. We also present an application of the superlattice sX-LDA method to [001] ordered InAs/InSb heterojunctions and superlattices. Band gaps and band offsets under strained conditions were directly calculated by sX-LDA without any experimental data as input. Slightly larger valence-band offsets than the LDA results, by about 0.08 eV, agree with the consequence of the GW calculations, indicating an increase of the potential negativity in the InAs region. This potential change along with the charge redistribution at the interface is found to be crucial to evaluate accurate band gaps of the superlattices.