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 calculat e self-consistent electronic structures for both occupied and unoccupied st ates. Considering nonuniform charge densities and local-field effects in th e z direction for FLM/SL, we have employed nonlocal Thomas-Fermi wave vecto rs to define the screened-exchange interaction. Three methods, for bulk, su perlattice, and film, have been implemented in the full-potential linearize d augmented plane wave method. The film sX-LDA method was then applied to t he Si(100)2x1 surface. The calculated occupied surface states show very goo d agreement with experiment. On the other hand, an underestimation of the c orrection to the unoccupied surface states, by about 0.2 eV, was estimated in comparison with available GW calculations. The ionization energy of Si w as evaluated with the film geometry to be 5.35 eV by virtue of the quasipar ticle corrections, showing good agreement with the experimental value of 5. 15 +/- 0.08 eV. Rie also present an application of the superlattice sX-LDA method to [001] ordered InAs/InSb heterojunctions and superlattices. Band g aps 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 redistribu tion at the interface is found to be crucial to evaluate accurate band gaps of the superlattices.