Parameter/topology editor and molecular simulator
Python Other
Clone or download
swails Merge pull request #1000 from jchodera/fix-patch-equivalence
Update logic for comparing OpenMM XML patches for equivalence
Latest commit 5885c44 Aug 8, 2018


Cross-program parameter and topology file editor and molecular mechanical simulator engine.


Build/Test Status Coverage Status


ParmEd is a package designed to facilitate creating and easily manipulating molecular systems that are fully described by a common classical force field. Supported force fields include Amber, CHARMM, AMOEBA, and several others that share a similar functional form (e.g., GROMOS).

ParmEd is capable of reading and writing to a wide array of different file formats, like the Amber topology and coordinate files, CHARMM PSF, parameter, topology, and coordinate files, Tinker parameter, topology, and coordinate files, and many others. The expressive central data structure (the Structure class) makes it easy to quickly and safely manipulate a chemical system, its underlying topology, and force field parameters describing its potential energy function.

There are two parts of ParmEd---a documented API that you can incorporate into your own Python scripts and programs, and a GUI/CLI pair of programs that provide a means to quickly perform various modifications to chemical systems for rapid prototyping.

The API also provides bindings to the OpenMM library, permitting you to carry out full molecular dynamics investigations using ParmEd on high-performant hardware, like AMD and NVidia GPUs.

Installing ParmEd

To install ParmEd, either clone this git repository or download the latest release and unpack the resulting tarball. This should create a new ParmEd source code directory. Change to that directory and build ParmEd with the command

python install

Note, if you are using the system Python, you may need to either run the above command as root (e.g., by using sudo) or add the --user flag to install it to your home directory. I would suggest the latter choice.

AMBER user can overwrite installed version by

python install --prefix=$AMBERHOME

Testing ParmEd

In order to automatically run the ParmEd tests, execute the following:

cd test
nosetests .


import parmed as pmd

# convert GROMACS topology to AMBER format
gmx_top = pmd.load_file('', xyz='pmaawaterFE20mer2.gro')'', format='amber')'pmaa.crd', format='rst7')

# convert AMBER topology to GROMACS, CHARMM formats
amber = pmd.load_file('prmtop', 'inpcrd')
# Save a GROMACS topology and GRO file'')'gromacs.gro')

# Save a CHARMM PSF and crd file'charmm.psf')'charmm.crd')

# convert mol2 to pdb file
mol2_parm = pmd.load_file('my.mol2')'my.pdb')

# and many more


Want to learn more? Visit the ParmEd documentation page at for examples, descriptions, and API documentation.

Authors and Contributors

The following people have contributed directly to the coding and validation efforts in ParmEd (in alphabetical order). And a special thanks to all of you who helped improve this project either by providing feedback, bug reports, or other general comments!

  • Jason Swails (principal developer) |

  • Carlos Hernandez

  • David L. Mobley

  • Hai Nguyen

  • Lee-Ping Wang

  • Pawel Janowski


                    LESSER GPL LICENSE INFO

Copyright (C) 2010 - 2014 Jason Swails

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
GNU General Public License for more details.

You should have received a copy of the GNU Lesser General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.

The `fortranformat` package is released under the MIT license, Copyright (C)
Brendan Arnold. See `fortranformat/` for more information.