The program now decides to use gmx_seq grompp over gmx grompp over srun -n 1 gmx_mpi grompp. In this way it prevents as much as possible calling srun. If you make the swarm grompps with srun the program calls slurm 500 times in the lapse of a second to do a job that lasts less than a second. This can make the slurm server unstable and you might get an email from your sysadmin asking what is going on.