$ sudo apt-get update
$ sudo apt-get install gromacs-openmpi 

gromacs-openmpi is installed in your system.

Make ensure the gromacs-openmpi package were installed using the commands given below,

$ sudo dpkg-query -l | grep gromacs-openmpi *

You will get with gromacs-openmpi package name, version, architecture and description in a table

gromacs-openmpi package basic information: