Using Amber force fields in GROMACS

Jason Swails' parmed program can make this an easy task. The first thing you need to do is create your prmtop and inpcrd files using tleap. After that, write a script (let's call it convert.py):

import parmed as pmd
parm = pmd.load_file('name-of-your.prmtop', 'name-of-your.inpcrd')
parm.save('gromacs.top')
parm.save('gromacs.gro')

Then run that program using the command

amber.python convert.py