# [gmx-users] Dielectric Constants

Size Zheng alexzheng42 at gmail.com
Tue Jun 5 08:37:32 CEST 2012

```Dear All,

I would like to calculate the dielectric constant of an ice crystal system in a simulation had about 1 ms.

I used g_dipoles command to do this. The obtained results seemed that they were only the values of the last frame in the simulation but not the average values,

Dipole moment (Debye)
---------------------
Average  =   2.1561  Std. Dev. =   0.2141  Error =   0.0000

The following averages for the complete trajectory have been calculated:

Total < M_x > = 2.50327 Debye
Total < M_y > = 37.9503 Debye
Total < M_z > = 70.9877 Debye

Total < M_x^2 > = 782.886 Debye^2
Total < M_y^2 > = 2080.37 Debye^2
Total < M_z^2 > = 6414.2 Debye^2

Total < |M|^2 > = 9277.45 Debye^2
Total |< M >|^2 = 6485.75 Debye^2

< |M|^2 > - |< M >|^2 = 2791.71 Debye^2

Finite system Kirkwood g factor G_k = 0.0977403
Infinite system Kirkwood g factor g_k = 0.0784452

Epsilon = 2.45241 (also the value of the last frame in the simulation, but not the average)

-------------------------------------

@ s0 legend "< |M|\S2\N >"
@ s1 legend "< |M| >\S2\N"
@ s2 legend "< |M|\S2\N > - < |M| >\S2\N"
@ s3 legend "< |M| >\S2\N / < |M|\S2\N >"

...
959880   9.278e+03  6.486e+03  2.791e+03  6.991e-01
959920   9.278e+03  6.486e+03  2.792e+03  6.991e-01
959960   9.278e+03  6.486e+03  2.792e+03  6.991e-01
960000   9.277e+03  6.486e+03  2.792e+03  6.991e-01

-------------------------------------

I also tried to use g_dielectric command, but never succeeded, and always got a message:

Fatal error:
nparm = 0 in file expfit.c, line 465

Is there any way that can obtain the average dielectric constants of the whole simulation? Or did I do something wrong?

Many thanks,

Size Zheng
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