g_velacc(1)					 GROMACS suite, VERSION 4.5.4-dev-20110404-bc5695c				       g_velacc(1)

NAME

       g_velacc - calculates velocity autocorrelation functions

       VERSION 4.5.4-dev-20110404-bc5695c

SYNOPSIS

       g_velacc  -f  traj.trr  -s topol.tpr -n index.ndx -o vac.xvg -[no]h -[no]version -nice int -b time -e time -dt time -[no]w -xvg enum -[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  calcu-
       lated.

       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

       -[no]versionno
	Print version 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

       -xvg enum xmgrace
	xvg plot formatting:  xmgrace,	xmgr or  none

       -[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,  exp9 or  erffit

       -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 until the end

SEE ALSO

       gromacs(7)

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

								  Mon 4 Apr 2011						       g_velacc(1)