Variational Formulation of theRMatrix Method for Multichannel Scattering

A variational treatment of the $R$ matrix method for multichannel scattering is given, in which basis functions used for expanding the wave function within a boundary radius $r_0$ need not satisfy specific boundary conditions at $r_0$. As an illustration, a simple basis set of monomial functions ($r^n,n=1,\dots ,N$) is used in a two-channel-model problem with long-range potentials. Excellent results are obtained with ten such functions in each channel.