PSTGF : time-independent R-Matrix atomic electron-impact code

TL;DR

This paper presents an updated, high-performance parallel version of the PSTGF code for electron-impact R-matrix calculations, incorporating modern features like MQDT options, improved load balancing, and GPU acceleration.

Contribution

It introduces a new, optimized PSTGF code that modernizes the original STGF with parallelism, MQDT integration, and GPU support for advanced atomic collision computations.

Findings

Enhanced computational efficiency on supercomputers

Integration of MQDT options with ICFT codes

Improved load balancing and vectorisation

Abstract

STGF is a community code employed for outer-region R-matrix calculations, describing electron-impact collisional processes. It is widely recognised that the original version of STGF was written by M. J. Seaton in 1983, but through constant refinement over the next decades by worldwide contributors has evolved into its current form that more reflects modern coding practice and current computer architectures. Despite its current wide acceptance, it was never formally published. Therefore, we present an updated high-performance parallel version of PSTGF, that balances the requirements of small university clusters, yet can exploit the computational power of cutting edge supercomputers. There are many improvements over the original STGF, but most noticeably, the full introduction of MQDT options that provide subsequent integration with ICFT (Intermediate Coupling Frame Transformation) codes, and for either Breit-Pauli / DARC (Dirac Atomic R-matrix Codes), better load balancing, high levels of vectorisation and simplified output. Semantically, the program is full fortran 90 in conjunction with MPI (Message Passing Interface) though has CUDA fortran options for the most numerically intensive code sections.