GMX-ORDER(1)

NAME
gmx-order - Compute the order parameter per atom for carbon tails

SYNOPSIS

    gmx order [-f [<.xtc/.trr/...>]] [-n [<.ndx>]] [-nr [<.ndx>]]
              [-s [<.tpr>]] [-o [<.xvg>]] [-od [<.xvg>]] [-ob [<.pdb>]]
              [-os [<.xvg>]] [-Sg [<.xvg>]] [-Sk [<.xvg>]]
              [-Sgsl [<.xvg>]] [-Sksl [<.xvg>]] [-b <time>] [-e <time>]
              [-dt <time>] [-[no]w] [-xvg <enum>] [-d <enum>] [-sl <int>]
              [-[no]szonly] [-[no]permolecule] [-[no]radial]
              [-[no]calcdist]

DESCRIPTION

gmx order computes the order parameter per atom for carbon tails. For atom i the vector i-1, i+1 is used together with an axis. The index file should contain only the groups to be used for calculations, with each group of equivalent carbons along the relevant acyl chain in its own group. There should not be any generic groups (like System, Protein) in the index file to avoid confusing the program (this is not relevant to tetrahedral order parameters however, which only work for water anyway).

gmx order can also give all diagonal elements of the order tensor and even calculate the deuterium order parameter Scd (default). If the option -szonly is given, only one order tensor component (specified by the -d option) is given and the order parameter per slice is calculated as well. If -szonly is not selected, all diagonal elements and the deuterium order parameter is given.

The tetrahedrality order parameters can be determined around an atom. Both angle an distance order parameters are calculated. See P.-L. Chau and A.J. Hardwick, Mol. Phys., 93, (1998), 511-518. for more details.

OPTIONS

Options to specify input files:

-f [<.xtc/.trr/...>] (traj.xtc)
    Trajectory: xtc trr cpt gro g96 pdb tng h5md

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

-nr [<.ndx>] (index.ndx) (Optional)
    Index file

-s [<.tpr>] (topol.tpr)
    Portable xdr run input file

    Options to specify output files:

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

-od [<.xvg>] (deuter.xvg)
    xvgr/xmgr file

-ob [<.pdb>] (eiwit.pdb) (Optional)
    Protein data bank file

-os [<.xvg>] (sliced.xvg)
    xvgr/xmgr file

-Sg [<.xvg>] (sg-ang.xvg) (Optional)
    xvgr/xmgr file

-Sk [<.xvg>] (sk-dist.xvg) (Optional)
    xvgr/xmgr file

-Sgsl [<.xvg>] (sg-ang-slice.xvg) (Optional)
    xvgr/xmgr file

-Sksl [<.xvg>] (sk-dist-slice.xvg) (Optional)
    xvgr/xmgr file

    Other options:

-b <time> (0)
    Time of first frame to read from trajectory (default unit ps)

-e <time> (0)
    Time of last frame to read from trajectory (default unit ps)

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

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

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

-d <enum> (z)
    Direction of the normal on the membrane: z, x, y

-sl <int> (1)
    Calculate order parameter as function of box length, dividing the box into this number of slices.

-[no]szonly (no)
    Only give Sz element of order tensor. (axis can be specified with -d)

-[no]permolecule (no)
    Compute per-molecule Scd order parameters

-[no]radial (no)
    Compute a radial membrane normal

-[no]calcdist (no)
    Compute distance from a reference

KNOWN ISSUES

•   This tool only works for saturated carbons and united atom force fields. For anything else, it is highly recommended to use a different analysis method!

•   The option -unsat claimed to do analysis for unsaturated carbons but this hasn't worked ever since it was added and has thus been removed.

SEE ALSO

gmx(1)

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