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       g_potential - calculates the electrostatic potential across the box

       VERSION 4.0.1


       g_potential  -f traj.xtc -n index.ndx -s topol.tpr -o potential.xvg -oc
       charge.xvg -of field.xvg -[no]h -nice int -b  time  -e  time  -dt  time
       -[no]w   -[no]xvgr  -d  string  -sl  int  -cb  int  -ce  int  -tz  real
       -[no]spherical -ng int -[no]correct


       Compute the electrostatical potential across  the  box.  The  potential
       iscalculated   by   first  summing  the  charges  per  slice  and  then
       integratingtwice of this charge distribution. Periodic  boundaries  are
       not taken  into account. Reference of potential is taken to be the left
       side ofthe box. It’s  also  possible  to  calculate  the  potential  in
       sphericalcoordinates   as   function  of  r  by  calculating  a  charge
       distribution inspherical slices and twice integrating  them.  epsilon_r
       is taken as 1,2 is more appropriate in many cases


       -f traj.xtc Input
        Trajectory: xtc trr trj gro g96 pdb cpt

       -n index.ndx Input
        Index file

       -s topol.tpr Input
        Run input file: tpr tpb tpa

       -o potential.xvg Output
        xvgr/xmgr file

       -oc charge.xvg Output
        xvgr/xmgr file

       -of field.xvg Output
        xvgr/xmgr file


        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)

        View output xvg, xpm, eps and pdb files

        Add  specific  codes  (legends  etc.)  in the output xvg files for the
       xmgrace program

       -d string Z
        Take the normal on the membrane in direction X, Y or Z.

       -sl int 10
        Calculate potential as function of boxlength, dividing the box  in  nr

       -cb int 0
        Discard first nr slices of box for integration

       -ce int 0
        Discard last nr slices of box for integration

       -tz real 0
        Translate all coordinates distance in the direction of the box

        Calculate spherical thingie

       -ng int 1
        Number of groups to consider

        Assume net zero charge of groups to improve accuracy


       - Discarding slices for integration should not be necessary.



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                                Thu 16 Oct 2008                 g_potential(1)