So I got a bit suspicious of all the compiler flags provided in the example Makefile after the problems with -ffast-math. A more minimal build command is simply:
gfortran -ffpe-summary=none -std=legacy -O3 LCModel.f -o lcmodel
My Windows box had gfortran (8.3.0) installed for R development and:
gfortran.exe -ffpe-summary=none -std=legacy -O3 LCModel.f -o LCModel.exe
works fine. Actually better than fine, the benchmark for the windows build from the LCModel website took 22 seconds, whereas the locally compiled version took 12.5s on an AMD Ryzen 5 3600. It’s possible the “official” build works better with Intel.
So close to a sub-second analysis!
Martin