Main Table of Contents

Fri 5 Jul 2013


g_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. The functional forms of the available functions are:

One parameter: y = exp(-a_1 x),
Two parameters: y = a_2 exp(-a_1 x),
Three parameters: y = a_2 exp(-a_1 x) + (1 - a_2) exp(-a_3 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 bool no Print help info and quit
-[no]version 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 bool no View output .xvg, .xpm, .eps and .pdb files
-xvg enum xmgrace xvg plot formatting: xmgrace, xmgr or none
-[no]fft bool no use fast fourier transform for correlation function
-[no]x1 bool yes use first column as x-axis rather than first data set
-eint real 5 Time 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 τ1
-tau2 real 1 Start value for fit parameter τ2
-eps0 real 80 ε0 of your liquid
-epsRF real 78.5 ε 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, exp9 or erffit
-nsmooth int 3 Number of points for smoothing