Cluster model of disordered systems : application to doped semiconductors and a simple model polymer

Sammanfattning: In this thesis we study with an extended cluster model calculation the combined effect of disorder and electron-electron interaction on the electronic structure of doped semiconductors and a simple model polymer chain. First a one-band model using a Hartree calculation is compared to other authors result for the impurity band using less realistic Hamiltonians. Secondly a two-band model using a Hartree-Fock calculation is presented. Thecalculated concentration depende nce of the electronic specific heat shows good agreement with the experimental findings. A modified Hartree-Fock scheme is then presented with the upper Hubbard band properly placed. Here it is shown that below the metal-nonmetal transition the one-particle wavefunctions are localized on statistically distributed clusters of impurity atoms. In the last part a stereo-irregular chain of h ydrogen atoms which simulates a model polymer is studied within the modified Hartree-Fock scheme. A detailed study of the localization properties of the wavefunctions is given with a combination of the information extracted from the inverse participation ratio and the moment ana lysis.