  The irregular solutions of the stationary Schr\"odinger equation are
important for the fundamental formal development of scattering theory. They are
also necessary for the analytical properties of the Green function, which in
practice can speed up calculations enormously. Despite these facts they are
seldom considered in numerical treatments. The reason for this is their
divergent behavior at the origin. This divergence demands high numerical
precision that is difficult to achieve, in particular, for non-spherical
potentials which lead to different divergence rates in the coupled angular
momentum channels. Based on an unconventional treatment of boundary conditions,
an integral-equation method is developed, which is capable to deal with this
problem. The available precision is illustrated by electron-density
calculations for NiTi in its monoclinic B19' structure.
