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NAME

       g_velacc - calculates velocity autocorrelation functions

       VERSION 4.0.1

SYNOPSIS

       g_velacc  -f traj.trr -s topol.tpr -n index.ndx -o vac.xvg -[no]h -nice
       int -b time -e time -dt time -[no]w -[no]xvgr -[no]m  -[no]mol  -acflen
       int  -[no]normalize  -P  enum  -fitfn  enum  -ncskip int -beginfit real
       -endfit real

DESCRIPTION

       g_velacc computes the velocity autocorrelation function.  When the   -m
       option is used, the momentum autocorrelation function is calculated.

       With option  -mol the velocity autocorrelation function of molecules is
       calculated. In this case the index group  should  consist  of  molecule
       numbers instead of atom numbers.

FILES

       -f traj.trr Input
        Full precision trajectory: trr trj cpt

       -s topol.tpr Input, Opt.
        Structure+mass(db): tpr tpb tpa gro g96 pdb

       -n index.ndx Input, Opt.
        Index file

       -o vac.xvg Output
        xvgr/xmgr file

OTHER OPTIONS

       -[no]hno
        Print help info and quit

       -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]wno
        View output xvg, xpm, eps and pdb files

       -[no]xvgryes
        Add  specific  codes  (legends  etc.)  in the output xvg files for the
       xmgrace program

       -[no]mno
        Calculate the momentum autocorrelation function

       -[no]molno
        Calculate the velocity acf of molecules

       -acflen int -1
        Length of the ACF, default is half the number of frames

       -[no]normalizeyes
        Normalize ACF

       -P enum 0
        Order of Legendre polynomial for ACF (0 indicates none):  0,  1,  2 or
       3

       -fitfn enum none
        Fit  function:   none,   exp,   aexp,   exp_exp,  vac,  exp5,  exp7 or
       exp9

       -ncskip int 0
        Skip N points in the output file of correlation functions

       -beginfit real 0
        Time where to begin the exponential fit of the correlation function

       -endfit real -1
        Time where to end the exponential fit of the correlation function,  -1
       is till the end

SEE ALSO

       gromacs(7)

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

                                Thu 16 Oct 2008                    g_velacc(1)