  We investigate the behavior of disordered interacting electrons in the
insulating regime. Our study is based on the quantum Coulomb glass model which
is obtained from the classical Coulomb glass by adding hopping matrix elements
between neighboring sites. We use two different numerical methods, viz. a
Hartree-Fock approximation and an exact diagonalization and compare the results
for the tunneling density of states and the localization properties in order to
determine the range of validity of the Hartree-Fock method. We find that the
Hartree-Fock method gives a good approximation for the density of states for
all energies but represents the localization properties correctly close to the
Fermi level only. Some consequences for the localization of disordered
interacting electrons are discussed.
