FARM - A FLEXIBLE ASYMPTOTIC R-MATRIX PACKAGE

The R-matrix formalism has been highly successful in describing a wide range of atomic and molecular scattering problems. A computational bottleneck in these calculations is the treatment of the scattering in the external region of configuration space where exchange effects may be neglected. A new package for solving this external region scattering problem is described. The package uses a combination of R-matrix propagation techniques to ensure optimum stability and efficiency in integrating the coupled Schrodinger equations. The radial distance over which the equations must be integrated is minimized by matching to an asymptotic wavefunction determined by an accelerated Gailitis expansion. The package is designed to provide accurate results with minimal input information and to be efficient for large systems of equations.