On dielectric response and quasiparticles in semiconductors and insulators

Some aspects of dielectric response pertinent to the calculation of quasiparticle energies are discussed. A new generalized plasmon-pole concept to treat the frequency dependence of the dielectric matrix is presented. The scheme based on the framework of the dielectric bandstructure implies a faster convergence when calculating the quasiparticle selfenergy. Moreover it has the merit that the dielectric matrix always has the correct analytical properties. To visualize the polarization cloud around a quasiparticle in a semiconductor the dielectric response for a test charge is studied. This leads to a natural subdivision of the electronic polarization in a semiconductor into charge transfer and dipolar polarization. The relative size of these contributions provides a measure for the importance of local field effects.