To extend a simulation create a modified .tpr file and use it with gmx mdrun:

Command:

$ gmx convert-tpr -s topol.tpr -extend time -o tpxout.tpr $ gmx mdrun -s tpxout.tpr -cpi state.cpt

Where time is how much longer to run the simulation in picoseconds, topol.tpr is the .tpr file associated with the original simulation, and state.cpt is the latest checkpoint file from that simulation. Instead of using -extend one can also use -until to specify the absolute ending time in picosecondes/nanoseconds. Check out the following Link:

https://wiki.archlinux.org/index.php/GROMACS

Hi Colleague

Find the following URL may help you:

http://www.bpc.uni-frankfurt.de/guentert/wiki/images/9/96/180627_AntwortenFragenTutorialMD.pdf

Regards...

e.g.

gmx convert-tpr -s md_0_1.tpr -extend 1000 -o md_0_2.tpr

gmx mdrun -v -nb gpu -deffnm md_0_2

The time is in ps (1000 ps is 1 microseg. as in the example).