| VERSION 4.5 |
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.
option | filename | type | description |
---|---|---|---|
-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 |
option | type | default | description |
---|---|---|---|
-[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 |