gmx-rdf(1) GROMACS Manual gmx-rdf(1)NAMEgmx-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 clos‐
est 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 dif‐
ferent 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, exclu‐
sions 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 con‐
tributions 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 ALSOgromacs(7)
More information about GROMACS is available at <http://www.gro‐
macs.org/>.
VERSION 5.0.6gmx-rdf(1)
