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# gmx-vanhove - Man Page

Compute Van Hove displacement and correlation functions

## Synopsis

```gmx vanhove [-f [<.xtc/.trr/...>]] [-s [<.tpr/.gro/...>]] [-n [<.ndx>]]
[-om [<.xpm>]] [-or [<.xvg>]] [-ot [<.xvg>]] [-b <time>]
[-e <time>] [-dt <time>] [-[no]w] [-xvg <enum>]
[-sqrt <real>] [-fm <int>] [-rmax <real>] [-rbin <real>]
[-mmax <real>] [-nlevels <int>] [-nr <int>] [-fr <int>]
[-rt <real>] [-ft <int>]```

## Description

gmx vanhove computes the Van Hove correlation function. The Van Hove G(r,t) is the probability that a particle that is at r_0 at time zero can be found at position r_0+r at time t. gmx vanhove determines G not for a vector r, but for the length of r. Thus it gives the probability that a particle moves a distance of r in time t. Jumps across the periodic boundaries are removed. Corrections are made for scaling due to isotropic or anisotropic pressure coupling.

With option -om the whole matrix can be written as a function of t and r or as a function of sqrt(t) and r (option -sqrt).

With option -or the Van Hove function is plotted for one or more values of t. Option -nr sets the number of times, option -fr the number spacing between the times. The binwidth is set with option -rbin. The number of bins is determined automatically.

With option -ot the integral up to a certain distance (option -rt) is plotted as a function of time.

For all frames that are read the coordinates of the selected particles are stored in memory. Therefore the program may use a lot of memory. For options -om and -ot the program may be slow. This is because the calculation scales as the number of frames times -fm or -ft. Note that with the -dt option the memory usage and calculation time can be reduced.

## Options

Options to specify input files:

-f [<.xtc/.trr/...>] (traj.xtc)

Trajectory: xtc trr cpt gro g96 pdb tng

-s [<.tpr/.gro/...>] (topol.tpr)

Structure+mass(db): tpr gro g96 pdb brk ent

-n [<.ndx>] (index.ndx) (Optional)

Index file

Options to specify output files:

-om [<.xpm>] (vanhove.xpm) (Optional)

X PixMap compatible matrix file

-or [<.xvg>] (vanhove_r.xvg) (Optional)

xvgr/xmgr file

-ot [<.xvg>] (vanhove_t.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

-sqrt <real> (0)

Use sqrt(t) on the matrix axis which binspacing # in sqrt(ps)

-fm <int> (0)

Number of frames in the matrix, 0 is plot all

-rmax <real> (2)

Maximum r in the matrix (nm)

-rbin <real> (0.01)

Binwidth in the matrix and for -or (nm)

-mmax <real> (0)

Maximum density in the matrix, 0 is calculate (1/nm)

-nlevels <int> (81)

Number of levels in the matrix

-nr <int> (1)

Number of curves for the -or output

-fr <int> (0)

Frame spacing for the -or output

-rt <real> (0)

Integration limit for the -ot output (nm)

-ft <int> (0)

Number of frames in the -ot output, 0 is plot all