First-Principles Theory of Quasiparticles: Calculation of Band Gaps in Semiconductors and Insulators

We present a first-principles theory for the quasiparticle energies of semiconductors and insulators. The full dielectric matrix is used to evaluate the nonlocal, energy-dependent electron self-energy operator. Both local-field effects and dynamical screening are found to be essential for understanding quasiparticle energies. Results for the band gaps, optical transitions, and band dispersions for silicon and diamond are in excellent agreement with existing experimental data.