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

gromacs-mpich is installed in your system.

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

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

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

gromacs-mpich package basic information: