A non-local extension of the Gaspari-Gyorffy theory for superconductors

We present a theory which extends the Gaspari-Gyorffy theory to include non-local corrections within the framework of the spherical rigid muffin tin approximation. We thereby construct an on-Fermi-sphere pseudopotential similar to that of the simple free electron metals. We apply our theory to Al and NbC for which²() andT_c are calculated. It turns out that for NbC the local approximation works well whereas for Al non-local corrections are important.