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    CHARMM (Chemistry at HARvard Macromolecular Mechanics) is a both a set of force fields and a software package for molecular dynamics simulations and analysis. Includes united atom (CHARMM19) and all atom (CHARMM22, CHARMM27, CHARMM36) force fields.  The CHARMM27 force field has been ported to GROMACS and is officially supported as of version 4.5.  CHARMM36 force field files can be obtained from the MacKerell lab website, which regularly produces up-to-date CHARMM force field files in GROMACS format.

    For using CHARMM36 in GROMACS 5.0 and newer, please use the following settings in the .mdp file:

    constraints = h-bonds
    cutoff-scheme = Verlet
    vdwtype = cutoff
    vdw-modifier = force-switch
    rlist = 1.2
    rvdw = 1.2
    rvdw-switch = 1.0
    coulombtype = PME
    rcoulomb = 1.2
    DispCorr = no

    Note that dispersion correction should be applied in the case of lipid monolayers, but not bilayers.

    Please also note that the switching distance is a matter of some debate in lipid bilayer simulations, and it is dependent to some extent on the nature of the lipid. Some studies have found that an 0.8-1.0 nm switch is appropriate, others argue 0.8-1.2 nm is best, and yet others stand by 1.0-1.2 nm. The user is cautioned to thoroughly investigate the force field literature for their chosen lipid(s) before beginning a simulation!

    Anyone using very old versions of GROMACS may find this script useful:

    • CHARMM to GROMACS - perl scripts intended to facilitate calculations using GROMACS programs and CHARMM forcefields (needed for GROMACS versions < 4.5).
    Page last modified 15:26, 6 Oct 2017 by JLemkul?