[gmx-users] question about dielectric constant calculation

[Lei Zhou]

Dear GMX-users,

I am trying to calculate the dieletric constant based on MD trajectories.
Two programs are used, g_dipoles and g_dielectric. I have the following
questions:

1) In g_dipoles, what number should I use for the flag  -epsilonRF? I used
PME duing MD simulation with the epsilon-r as 1 and epsilon-surface as 0.
2) What other flags are critical for calculation, like -P,  Order of
Legendre polynomial for ACF?
3) Based on the manual, the epsilon calculated by g_dielectric is
frenquency-related. How about the epsilon output from g_dipoles and the
relationship to difference frenquencies?
4) I used the output from g_dipoles, Mtot.xvg, as an input for g_dielectric.
Here is the command used: g_dielectric -f Mtot.xvg, however, I got the
following error messages after frame 49: Fatal error: nparm = 0 in file
expfit.c, line 462.

I am really grateful for any help with those questions. Thank you.

Lei Zhou
Columbia University
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