A.G. Sunderland

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

Abstract 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.

Electron impact excitation of Fe III : forbidden transitions

Electron-impact excitation collision strengths of the iron peak element Fe III are calculated in the close-coupling approximation using the new R-matrix program PRMAT designed for present and future generations of parallel processors. In the present calculations 136 LS-coupled states arising from the 3d6, 3d54s and 3d54p configurations of Fe III are retained. The effective collision strengths, which are extremely important in the analysis of astrophysically important lines in the Fe III spectra, are obtained by averaging the electron collision strengths for a wide range of incident electron energies over a Maxwellian distribution of velocities. Results are presented for electron temperatures (Te in Kelvin) in the range 3.3≤log Te≤6.0, applicable to many laboratory and astrophysical plasmas for forbidden transitions within the 3d6 manifold. The present results provide improved results for important lines in the Fe III spectrum.

Parallelization of Atomic R-Matrix Scattering Programs

R-matrix theory has been the basis of computer programs that have described a wide range of atomic, molecular, optical and surface processes for more than twenty-five years1. These processes now include electron scattering by atoms, ions and molecules, atomic and molecular photoionization, free-free transitions, atomic and molecular multiphoton processes, positron scattering by atoms and molecules, electron scattering by molecules physisorbed on surfaces and electron energy loss in transition metal oxides. The R-matrix programs written to describe these processes have been used to calculate data of importance in many applications including those in laser physics, controlled thermonuclear fusion and plasma physics, atmospheric physics and chemistry and astronomy2. These programs are now used world-wide and have formed the basis of several international collaborations including most notably the international Opacity Project3.