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gmx-rdf(1)                      GROMACS Manual                      gmx-rdf(1)

NAME
       gmx-rdf - Calculate radial distribution functions

SYNOPSIS
       gmx rdf [-f [<.xtc/.trr/...>]] [-s [<.tpr/.tpb/...>]] [-n [<.ndx>]]
               [-o [<.xvg>]] [-cn [<.xvg>]] [-hq [<.xvg>]] [-nice <int>]
               [-b <time>] [-e <time>] [-dt <time>] [-[no]w] [-xvg <enum>]
               [-bin <real>] [-[no]com] [-surf <enum>] [-rdf <enum>]
               [-[no]pbc] [-[no]norm] [-[no]xy] [-cut <real>] [-ng <int>]
               [-fade <real>]

DESCRIPTION
       The structure of liquids can be studied by either neutron or X-ray
       scattering. The most common way to describe liquid structure is by a
       radial distribution function. However, this is not easy to obtain from
       a scattering experiment.

       gmx rdf calculates radial distribution functions in different ways. The
       normal method is around a (set of) particle(s), the other methods are
       around the center of mass of a set of particles (-com) or to the
       closest particle in a set (-surf). With all methods, the RDF can also
       be calculated around axes parallel to the z-axis with option -xy. With
       option -surf normalization can not be used.

       The option -rdf sets the type of RDF to be computed. Default is for
       atoms or particles, but one can also select center of mass or geometry
       of molecules or residues. In all cases, only the atoms in the index
       groups are taken into account. For molecules and/or the center of mass
       option, a run input file is required. Weighting other than COM or COG
       can currently only be achieved by providing a run input file with
       different masses. Options -com and -surf also work in conjunction with
       -rdf.

       If a run input file is supplied (-s) and -rdf is set to atom,
       exclusions defined in that file are taken into account when calculating
       the RDF. The option -cut is meant as an alternative way to avoid
       intramolecular peaks in the RDF plot. It is however better to supply a
       run input file with a higher number of exclusions. For e.g. benzene a
       topology, setting nrexcl to 5 would eliminate all intramolecular
       contributions to the RDF. Note that all atoms in the selected groups
       are used, also the ones that don't have Lennard-Jones interactions.

       Option -cn produces the cumulative number RDF, i.e. the average number
       of particles within a distance r.

OPTIONS
       Options to specify input and output files:

       -f [<.xtc/.trr/...>] (traj.xtc) (Input)
           Trajectory: xtc trr cpt trj gro g96 pdb tng

       -s [<.tpr/.tpb/...>] (topol.tpr) (Input, Optional)
           Structure+mass(db): tpr tpb tpa gro g96 pdb brk ent

       -n [<.ndx>] (index.ndx) (Input, Optional)
           Index file

       -o [<.xvg>] (rdf.xvg) (Output)
           xvgr/xmgr file

       -cn [<.xvg>] (rdf_cn.xvg) (Output, Optional)
           xvgr/xmgr file

       -hq [<.xvg>] (hq.xvg) (Output, Optional)
           xvgr/xmgr file

       Other options:

       -nice <int> (19)
           Set the nicelevel

       -b <time> (0)
           First frame (ps) to read from trajectory

       -e <time> (0)
           Last frame (ps) to read from trajectory

       -dt <time> (0)
           Only use frame when t MOD dt = first time (ps)

       -[no]w  (no)
           View output .xvg, .xpm, .eps and .pdb files

       -xvg <enum> (xmgrace)
           xvg plot formatting: xmgrace, xmgr, none

       -bin <real> (0.002)
           Binwidth (nm)

       -[no]com  (no)
           RDF with respect to the center of mass of first group

       -surf <enum> (no)
           RDF with respect to the surface of the first group: no, mol, res

       -rdf <enum> (atom)
           RDF type: atom, mol_com, mol_cog, res_com, res_cog

       -[no]pbc  (yes)
           Use periodic boundary conditions for computing distances. Without
       PBC the maximum range will be three times the largest box edge.

       -[no]norm  (yes)
           Normalize for volume and density

       -[no]xy  (no)
           Use only the x and y components of the distance

       -cut <real> (0)
           Shortest distance (nm) to be considered

       -ng <int> (1)
           Number of secondary groups to compute RDFs around a central group

       -fade <real> (0)
           From this distance onwards the RDF is tranformed by g'(r) = 1 +
       [g(r)-1] exp(-(r/fade-1)2 to make it go to 1 smoothly. If fade is 0.0
       nothing is done.

SEE ALSO
       gromacs(7)

       More information about GROMACS is available at
       <http://www.gromacs.org/>.

VERSION 5.0.6                                                       gmx-rdf(1)