You've simulated longer than you're asking mdrun to run. If you've already done 200,000,000 steps, then telling it to now run for a total of 100,000,000 steps and starting from a point in the future makes no sense, so the program exits.

Justin Lemkul Thank you for your reply. I just want to continue from 200,000,000 steps and add another 100,000,000 steps. Do you have any idea on how to do that? This is the only Gromacs version that I encounted this problem on. On other versions, my system is able to reach 500 ns without any problem.

check this link: it is too simple to do.

http://www.gromacs.org/Documentation/Howtos/Extending_Simulations

Please see the link Zana Pirkhezranian provided. The mdrun -nsteps argument (which actually no longer exists) is a development tool to override the number of steps in the .tpr file and is only for testing. It signifies the *total* number of steps to run, and is not intended for extensions.

Dear @Justin Lemkul

pls see

http://www.gromacs.org/Documentation/How-tos/Extending_Simulations

Zana Pirkhezranian yes, I'm familiar with the content, having written much of it myself :) I was pointing out to the OP that there is useful information there.

I should also note, however, that the documentation on gromacs.org is outdated and no longer updated. The current link is http://manual.gromacs.org/current/user-guide/managing-simulations.html#extending-a-tpr-file (note that tpbconv no longer exists, it is gmx convert-tpr).

@Justin you're right. now convert-tpr is valid . thanks for your information.