  We apply the Coherent Potential Approximation (CPA) to a simple extended
Hubbard model with a nearest and next nearest neighbour hopping for disordered
superconductors with s-, d- and p-wave pairing. We show how the Van Hove
singularities in the electron density of states enhance the transition
temperature Tc for exotic superconductors in a clean and weakly disordered
system. The Anderson theorem and pair-breaking effects in presence of Van Hove
singularity caused by non-magnetic disorder are also discussed.
