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GMX-H2ORDER(1)			    GROMACS			GMX-H2ORDER(1)

NAME
       gmx-h2order - Compute the orientation of	water molecules

SYNOPSIS
	  gmx h2order [-f [<.xtc/.trr/...>]] [-n [<.ndx>]] [-nm	[<.ndx>]]
		      [-s [<.tpr>]] [-o	[<.xvg>]] [-b <time>] [-e <time>]
		      [-dt <time>] [-[no]w] [-xvg <enum>] [-d <enum>]
		      [-sl <int>]

DESCRIPTION
       gmx h2order computes the	orientation of water molecules with respect to
       the normal of the box. The program determines the average cosine	of the
       angle  between  the  dipole moment of water and an axis of the box. The
       box is divided in slices	and  the  average  orientation	per  slice  is
       printed.	  Each	water molecule is assigned to a	slice, per time	frame,
       based on	the position of	the oxygen. When -nm is	used,  the  angle  be-
       tween the water dipole and the axis from	the center of mass to the oxy-
       gen  is	calculated  instead  of	the angle between the dipole and a box
       axis.

OPTIONS
       Options to specify input	files:

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

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

       -nm [<.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

       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)
	      Take the normal on the membrane in direction X, Y	or Z.: Z, Y, X

       -sl <int> (0)
	      Calculate	order parameter	as function of boxlength, dividing the
	      box in this number of slices.

KNOWN ISSUES
        The program assigns whole water molecules to a	slice,	based  on  the
	 first	atom  of  three	 in  the index file group. It assumes an order
	 O,H,H.	Name is	not important, but the order is. If this demand	is not
	 met, assigning	molecules to slices is different.

SEE ALSO
       gmx(1)

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

COPYRIGHT
       2025, GROMACS development team

2025.0				 Feb 10, 2025			GMX-H2ORDER(1)

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