  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.
