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GMX-CURRENT(1)			     GROMACS			  GMX-CURRENT(1)

NAME
     gmx-current  -  Calculate	dielectric constants and current autocorrelation
     function

SYNOPSIS
	gmx current [-s [<.tpr/.gro/...>]] [-n [<.ndx>]] [-f [<.xtc/.trr/...>]]
		    [-o [<.xvg>]] [-caf [<.xvg>]] [-dsp [<.xvg>]]
		    [-md [<.xvg>]] [-mj [<.xvg>]] [-mc [<.xvg>]] [-b <time>]
		    [-e <time>] [-dt <time>] [-[no]w] [-xvg <enum>]
		    [-sh <int>] [-[no]nojump] [-eps <real>] [-bfit <real>]
		    [-efit <real>] [-bvit <real>] [-evit <real>]
		    [-temp <real>]

DESCRIPTION
     gmx current is a tool for calculating the current autocorrelation function,
     the correlation of the rotational and translational dipole  moment  of  the
     system,  and  the resulting static dielectric constant. To obtain a reason-
     able result, the index group has to be neutral.  Furthermore,  the  routine
     is  capable of extracting the static conductivity from the current autocor-
     relation  function,  if  velocities  are  given.  Additionally,   an   Ein-
     stein-Helfand fit can be used to obtain the static conductivity.

     The flag -caf is for the output of the current autocorrelation function and
     -mc  writes the correlation of the rotational and translational part of the
     dipole moment in the corresponding  file.	However,  this	option	is  only
     available	for trajectories containing velocities.  Options -sh and -tr are
     responsible for the averaging and integration of the autocorrelation  func-
     tions.  Since averaging proceeds by shifting the starting point through the
     trajectory, the shift can be modified with -sh to enable the choice of  un-
     correlated  starting  points. Towards the end, statistical inaccuracy grows
     and integrating the correlation function only yields reliable values  until
     a certain point, depending on the number of frames. The option -tr controls
     the  region  of  the integral taken into account for calculating the static
     dielectric constant.

     Option -temp sets the temperature required for the computation of the  sta-
     tic dielectric constant.

     Option  -eps controls the dielectric constant of the surrounding medium for
     simulations using a Reaction Field or dipole corrections of the Ewald  sum-
     mation (-eps=0 corresponds to tin-foil boundary conditions).

     -[no]nojump  unfolds  the	coordinates to allow free diffusion. This is re-
     quired to get a continuous translational dipole moment,  required	for  the
     Einstein-Helfand  fit.  The results from the fit allow the determination of
     the dielectric constant for system of charged  molecules.	However,  it  is
     also  possible  to extract the dielectric constant from the fluctuations of
     the total dipole moment in folded coordinates. But this option  has  to  be
     used  with care, since only very short time spans fulfill the approximation
     that the density of the molecules is approximately constant and  the  aver-
     ages are already converged. To be on the safe side, the dielectric constant
     should  be  calculated with the help of the Einstein-Helfand method for the
     translational part of the dielectric constant.

OPTIONS
     Options to specify input files:

     -s [<.tpr/.gro/...>] (topol.tpr)
	    Structure+mass(db): tpr gro g96 pdb brk ent

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

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

     Options to specify output files:

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

     -caf [<.xvg>] (caf.xvg) (Optional)
	    xvgr/xmgr file

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

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

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

     -mc [<.xvg>] (mc.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

     -sh <int> (1000)
	    Shift of the frames for averaging the correlation functions and  the
	    mean-square displacement.

     -[no]nojump (yes)
	    Removes jumps of atoms across the box.

     -eps <real> (0)
	    Dielectric constant of the surrounding medium. The value zero corre-
	    sponds to infinity (tin-foil boundary conditions).

     -bfit <real> (100)
	    Begin  of  the  fit  of the straight line to the MSD of the transla-
	    tional fraction of the dipole moment.

     -efit <real> (400)
	    End of the fit of the straight line to the MSD of the  translational
	    fraction of the dipole moment.

     -bvit <real> (0.5)
	    Begin of the fit of the current autocorrelation function to a*t^b.

     -evit <real> (5)
	    End of the fit of the current autocorrelation function to a*t^b.

     -temp <real> (300)
	    Temperature for calculating epsilon.

SEE ALSO
     gmx(1)

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

COPYRIGHT
     2026, GROMACS development team

2026.3				  Jun 25, 2026			  GMX-CURRENT(1)
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