A CONCEPT FOR IMPROVING THE EFFICIENCY OF R-MATRIX CALCULATIONS FOR ELECTRON MOLECULE-SCATTERING

In R-matrix calculations of electron-molecule scattering, matrix elements of the Hamiltonian operator are required in the form of integrals confined to a sphere-OMEGA around the target system. Evaluation of these integrals is a computational bottleneck, especially for polyatomic molecules. In this article we introduce a method in which integrals over OMEGA are replaced by integrals over the entire coordinate space. This technique allows the use of standard integral programs, developed for bound-state molecular calculations, which are of high efficiency. Such integrals are modified in a subsequent step by subtracting their contribution outside OMEGA. Hereby we take advantage of a basic assumption, in R-matrix theory, that the potential outside of OMEGA can be approximated by multipole potentials due to specified electronic target states. The applicability of the method is demonstrated and discussed for the resonant scattering process related to the metastable 2-PI(g) state of N(-)2. These calculations are restricted to fixed-nuclei electron scattering.