[gmx-users] -multidir option in REMD (GROMACS v2016.1)

[ABEL Stephane]

Dear all, 

I would like to do a REMD of a system with 75 replicas (with 75 directories named md_0,..., md_75) and I have two questions. 

1) To launch the md calculation we should use the followng command : 

mpirun -np 4 mdrun_mpi -v -multidir sim[0123] -replex XXX

My question is since I have 75 replicas (directories). How I should set the argument of -multidir ? Like this : -multidir md_[01234...75] or only "md_". 

I have used the following command : mdrun_mpi -v -multidir ./"$Stage1_FileName"/md_ -replex 500, but the program stops with the following error : Need at least two replicas for replica exchange (option -multi)

2) Second question It is not clear to me how I should set the number of step in the mdp file of each replica use in the production runs.  For instance I want to do a simulation of 50 ns, should I set nsteps = 5000000/75

Could you help me ? 

Thanks for your help

Stéphane