Modified mott-hubbard-anderson model results of an unrestricted hartree-fock pseudocluster calculation

Abstract
We have performed a pseudocluster calculation to show that while the MHA model for doped semiconductors is valid for very low impurity concentrations (NN c/2, N c = critical concentration), the donor-excitonic states are important in the regime N c/2 < N < N c where the upper Hubbard band is almost pushed into the conduction band. We have also calculated the linear specific heat in the insulating region and found excellent agreement with experimental data.