A fast converging separable expansion for realistic nuclear potentials

A new separable-expansion method for realistic multichannel scattering problems is proposed. The approximate finite-rank potentials are obtained by resorting to a complete set of sturmians referring to a fixed negative energy. These basis functions are solutions of a coupled-channel auxiliary eigenvalue problem embodying the main physical features of the original interactions. The coupled sturmian equations are solved through a simple diagonalization procedure by employing another set of auxiliary sturmians given in closed analytic form. The method is applied to uncoupled as well as to coupled states for the Reid potential. Good convergence properties are found both on and off the energy shell. The method can be applied to general coupled-channel problems, and can be extended so as to treat absorptive and/or energy-dependent interactions