Collective variables module (Colvars)

A software module for molecular simulation and analysis that provides a high-performance implementation of sampling algorithms defined on a reduced space of continuously differentiable functions (aka collective variables).

The module itself implements a variety of functions and algorithms, including free-energy estimators based on thermodynamic forces, non-equilibrium work and probability distributions.

Obtaining and using

The easiest way to obtain pre-compiled versions of Colvars is via one of following:

• the molecular simulation program LAMMPS;
• the molecular simulation program NAMD;
• the molecular visualization program VMD.

Please check here to see which version of Colvars is included with the round-number or "stable" versions of each code.

Documentation

The Colvars webpage includes user documentation for the three codes, as well as a Doxygen-based developer documentation.

The reference article is: G. Fiorin, M. L. Klein, and J. Hénin, Molecular Physics 111, 3345 (2013).
https://dx.doi.org/10.1080/00268976.2013.813594 [BibTex file] [Endnote file]

Example input

Colvars requires a configuration file, or alternatively configuration arguments given through scripting commands by the linked program.

• In NAMD:

colvars on
cv configfile <Colvars configuration file>

• In VMD (Tip: try also the new "Colvars Dashboard" plugin):

cv molid top
cv configfile <Colvars configuration file>

• In LAMMPS:

fix Colvars all colvars configfile <Colvars configuration file>

The contents of the configuration file are typically the same across all programs, for example:

colvar { # Define a new variable
  name d # Must give a name to this variable
  width 0.2 # Estimated fluctuation amplitude and/or grid resolution, "w_d"
  distance { # This variable is a distance between centers of mass (COMs)
    group1 { atomNumbers 1 2 3 } # List the atoms of the 1st group
    group2 { atomNumbers 4 5 6 } # List the atoms of the 2nd group
  }
}

harmonic { # Define a harmonic potential, 1/2*K*(d-d0)^2/w_d^2
  colvars d # Apply it to the variable "d"
  centers 5.0 # The center of the potential, "d0"
  forceConstant 10.0 # Force constant, "K"
}

Complete input decks for some of the most commonly used features are available in the examples repository: https://github.com/Colvars/examples

See also the examples folder of this repository for other examples of configurations. Configuration options (particularly, the selections of atoms) require minimal changes to reflect the specifics of each simulation.

The tests folder also contains functional segments of Colvars configuration, used to build numerical tests of code accuracy and stability. Feel free to use these segments in your production runs.

Updating to the latest version

To recompile each program with the most recent version of the module, download the master branch of this repository, or clone it via git:

git clone https://github.com/Colvars/colvars.git

and run the provided update-colvars-code.sh script against the unpacked source tree of any of the supported programs:

./update-colvars-code.sh /path/to/lammps           ; # updates LAMMPS
./update-colvars-code.sh /path/to/NAMD_X.YY_Source ; # updates NAMD
./update-colvars-code.sh /path/to/vmd-X.Y.Z        ; # updates VMD
./update-colvars-code.sh /path/to/vmd-plugins      ; # updates VMD plugins

and recompile them.

The update-colvars-code.sh script and its supporting files are synchronized with the latest version of each program:

• the LAMMPS Github repository;
• the NAMD Git repository;
• the CVS repositories of VMD and its plugins.

Earlier versions are not supported.

Which version is recommended?

The master branch is to be considered the "stable" release at any given time; any bugfixes are released through master first. The input syntax is near-completely backward-compatible and output files are forward-compatible. Feel free to download Colvars and update NAMD, VMD or LAMMPS as needed.

Other branches are dedicated to the development of specific features: please use them at your own discretion.

Feedback

Please use the "Issues" tab of this page to submit new bug reports or to suggest new features.

License

This software is distributed under the GNU Lesser General Public License, version 3. See COPYING.LESSER for complete licensing terms.