  We investigate the single-impurity Anderson model by means of the recently
introduced modified perturbation theory. This approximation scheme yields
reasonable results away from the symmetric case. The agreement with exactly
known results for the symmetric case is checked, and results for the
non-symmetric case are presented. With decreasing conduction band occupation,
the breakdown of the screening of the local moment is observed. In the
crossover regime between Kondo limit and mixed-valence regime, an enhanced
zero-temperature susceptibility is found.
