Castep is written entirely in Fortran 90, and HECToR has three Fortran 90 compilers available: Portland Group (pgf90), Pathscale (pathf90) and GNU's gfortran. Following the benchmarking carried out during the procurement exercise, it was anticipated that Pathscale's pathf90 compiler would be the compiler of choice and Alan Simpson (EPCC) was kind enough to provide his flags for the Pathscale compiler, based on the ones Cray used in the procurement:
-O3 -OPT:Ofast -OPT:recip=ON -OPT:malloc_algorithm=1 -inline -INLINE:preempt=ON
Note that this switches on fast-math.
Unless otherwise noted, all program development and benchmarking was performed with the Castep 4.2 codebase, as shipped to the United Kingdom Car-Parinello (UKCP) consortium, which was the most recent release of Castep at the commencement of this dCSE project and was the version available on HECToR to end-users.