Main Table of Contents

Thu 26 Aug 2010


dielectric calculates frequency dependent dielectric constants from the autocorrelation function of the total dipole moment in your simulation. This ACF can be generated by g_dipoles. For an estimate of the error you can run g_statistics on the ACF, and use the output thus generated for this program. The functional forms of the available functions are:

One parameter : y = Exp[-a1 x], Two parameters : y = a2 Exp[-a1 x], Three parameters: y = a2 Exp[-a1 x] + (1 - a2) Exp[-a3 x]. Start values for the fit procedure can be given on the command line. It is also possible to fix parameters at their start value, use -fix with the number of the parameter you want to fix.

Three output files are generated, the first contains the ACF, an exponential fit to it with 1, 2 or 3 parameters, and the numerical derivative of the combination data/fit. The second file contains the real and imaginary parts of the frequency-dependent dielectric constant, the last gives a plot known as the Cole-Cole plot, in which the imaginary component is plotted as a function of the real component. For a pure exponential relaxation (Debye relaxation) the latter plot should be one half of a circle.


-f dipcorr.xvg Input xvgr/xmgr file
-d deriv.xvg Output xvgr/xmgr file
-o epsw.xvg Output xvgr/xmgr file
-c cole.xvg Output xvgr/xmgr file

Other options

-[no]h gmx_bool no Print help info and quit
-[no]version gmx_bool no 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]w gmx_bool no View output xvg, xpm, eps and pdb files
-xvg enum xmgrace xvg plot formatting: xmgrace, xmgr or none
-[no]fft gmx_bool no use fast fourier transform for correlation function
-[no]x1 gmx_bool yes use first column as X axis rather than first data set
-eint real 5 Time were to end the integration of the data and start to use the fit
-bfit real 5 Begin time of fit
-efit real 500 End time of fit
-tail real 500 Length of function including data and tail from fit
-A real 0.5 Start value for fit parameter A
-tau1 real 10 Start value for fit parameter tau1
-tau2 real 1 Start value for fit parameter tau2
-eps0 real 80 Epsilon 0 of your liquid
-epsRF real 78.5 Epsilon of the reaction field used in your simulation. A value of 0 means infinity.
-fix int 0 Fix parameters at their start values, A (2), tau1 (1), or tau2 (4)
-ffn enum none Fit function: none, exp, aexp, exp_exp, vac, exp5, exp7 or exp9
-nsmooth int 3 Number of points for smoothing