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Theory and Calculations of the Electronic Structure of Solids Having Directional Bonding.

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Final rept.,

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The self-consistent electronic structure of Si, Ge, and zinc-blende GaP, GaAs, ZnS and ZnSe were determined using the linear combination of Gaussian orbitals method which was just developed. A completely general form of the spatial dependence of the potential was used to describe accurately the bonding character in the tetrahedral environment. The ground state charge densities we determined agree very well with experiment where available as do the locations of the valence bands, energies, and effective masses. A striking result is that the optical band gaps are underestimated by approximately 30 or more, although the general conduction-band topology is good. This is an inherent difficulty of using the local density approximation for the exchange correlation potential a theory of the ground state properties to describe the excitation energies. The interband optical properties of Si, Ge, GaP, GaAs, ZnS, and ZnSe were calculated using our self-consistent energies and wave functions. Qualitatively good agreement with experiment is found. Agreement with experiment with regard to line shapes and peak positions can be improved using an empirical energy dependent self-energy correction as appears in the Sham-Kohn local density theory of excitation. Our results clearly pointed up the urgent need of an improved theory of the excitation energies in semiconductors and insulators which is being actively pursued.

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  • Atomic and Molecular Physics and Spectroscopy
  • Solid State Physics

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