A parallel R-matrix program PRMAT for electron–atom and electron–ion scattering calculations Original Research Article

This paper describes a new parallel R-matrix program PRMAT which enables very large electron–atom and electron–ion scattering calculations of importance in many applications to start to be addressed for the first time on the current generation of massively parallel computers. The paper commences with an overview of R-matrix theory applied to electron–atom and electron–ion scattering, in which the fundamental concepts and the basic equations of the theory are given. A detailed description of this new parallel program PRMAT is then given and its relation to earlier scalar programs RMATRXII and FARM, which treat respectively the internal and external R-matrix regions, is discussed. Of particular importance is the development of a new parallel spin-splitting algorithm and program which takes advantage of the spin de-coupling of the scattering channels in the external and asymptotic R-matrix regions where electron exchange and correlation effects are negligible. A detailed description of the allocation of processor nodes to the various parallel tasks is given and illustrative timings on a Cray T3E-1200 parallel supercomputer are given. Finally the paper concludes by describing an illustrative electron–NiIV ion scattering calculation of importance in the analysis of astronomical spectra. Converged effective collision strengths for some forbidden transitions are reported which involve the solution of cases with more than 300 coupled channels requiring the calculation of collision strengths at over 15,000 energy values.