Well, I don't know 'mprun'. In linux with MPI, you do: grompp -np 10 -shuffle -sort [...] mpirun -np 10 mdrun_mpi [same as mdrun] Cheers, Alan -- -------------------------- Alan Wilter Sousa da Silva -------------------------- D.Sc. - IBCCF/UFRJ Projeto BioPAUA - HP/LNCC Petrópolis (RJ), Brasil www.lncc.br/~alan