1 .TH g_current 1 "Thu 16 Oct 2008"
3 g_current - calculates dielectric constants for charged systems
11 .BI "-o" " current.xvg "
12 .BI "-caf" " caf.xvg "
13 .BI "-dsp" " dsp.xvg "
34 This is a tool for calculating the current autocorrelation function, the correlation
35 of the rotational and translational dipole moment of the system, and the resulting static
36 dielectric constant. To obtain a reasonable result the index group has to be neutral.
37 Furthermore the routine is capable of extracting the static conductivity from the current
38 autocorrelation function, if velocities are given. Additionally an Einstein-Helfand fit also
39 allows to get the static conductivity.
44 is for the output of the current autocorrelation function and
47 correlation of the rotational and translational part of the dipole moment in the corresponding
48 file. However this option is only available for trajectories containing velocities.Options
52 are responsible for the averaging and integration of the
53 autocorrelation functions. Since averaging proceeds by shifting the starting point
54 through the trajectory, the shift can be modified with
56 to enable the choice of uncorrelated
57 starting points. Towards the end, statistical inaccuracy grows and integrating the
58 correlation function only yields reliable values until a certain point, depending on
59 the number of frames. The option
61 controls the region of the integral taken into account
62 for calculating the static dielectric constant.
68 sets the temperature required for the computation of the static dielectric constant.
73 controls the dielectric constant of the surrounding medium for simulations using
74 a Reaction Field or dipole corrections of the Ewald summation (eps=0 corresponds to
75 tin-foil boundary conditions).
81 unfolds the coordinates to allow free diffusion. This is required to get a continuous
82 translational dipole moment, required for the Einstein-Helfand fit. The resuls from the fit allow to
83 determine the dielectric constant for system of charged molecules. However it is also possible to extract
84 the dielectric constant from the fluctuations of the total dipole moment in folded coordinates. But this
85 options has to be used with care, since only very short time spans fulfill the approximation, that the density
86 of the molecules is approximately constant and the averages are already converged. To be on the safe side,
87 the dielectric constant should be calculated with the help of the Einstein-Helfand method for
88 the translational part of the dielectric constant.
92 Structure+mass(db): tpr tpb tpa gro g96 pdb
100 Trajectory: xtc trr trj gro g96 pdb cpt
102 .BI "-o" " current.xvg"
106 .BI "-caf" " caf.xvg"
110 .BI "-dsp" " dsp.xvg"
128 Print help info and quit
130 .BI "-nice" " int" " 0"
133 .BI "-b" " time" " 0 "
134 First frame (ps) to read from trajectory
136 .BI "-e" " time" " 0 "
137 Last frame (ps) to read from trajectory
139 .BI "-dt" " time" " 0 "
140 Only use frame when t MOD dt = first time (ps)
143 View output xvg, xpm, eps and pdb files
145 .BI "-[no]xvgr" "yes "
146 Add specific codes (legends etc.) in the output xvg files for the xmgrace program
148 .BI "-sh" " int" " 1000"
149 Shift of the frames for averaging the correlation functions and the mean-square displacement.
151 .BI "-[no]nojump" "yes "
152 Removes jumps of atoms across the box.
154 .BI "-eps" " real" " 0 "
155 Dielectric constant of the surrounding medium. eps=0.0 corresponds to eps=infinity (thinfoil boundary conditions).
157 .BI "-bfit" " real" " 100 "
158 Begin of the fit of the straight line to the MSD of the translational fraction of the dipole moment.
160 .BI "-efit" " real" " 400 "
161 End of the fit of the straight line to the MSD of the translational fraction of the dipole moment.
163 .BI "-bvit" " real" " 0.5 "
164 Begin of the fit of the current autocorrelation function to a*tb.
166 .BI "-evit" " real" " 5 "
167 End of the fit of the current autocorrelation function to a*tb.
169 .BI "-tr" " real" " 0.25 "
170 Fraction of the trajectory taken into account for the integral.
172 .BI "-temp" " real" " 300 "
173 Temperature for calculating epsilon.