[gmx-users] Some suggestions about the gmx current tool

Mahsa ebadi.mahsa at gmail.com
Wed Jun 12 15:12:52 CEST 2019

Hi gmx-users,

I use gmx current tool to calculate static conductivity by version 2018:

gmx current -f md.xtc -o -dsp -md -mj -temp 423 -nojump -n index.ndx -s

Indeed the tool is useful, but I think some parts in the output are
confusing and need to be improved.
I think the generated dsp.xvg file which reports the MSD of translational
dipole moments vs time has the wrong unit in the plot. The unit should be
(S/m) ps according to this equation:
[image: Screen Shot 2019-06-12 at 14.35.45.png]
and the pre-factor fit reported in the output of dsp.xvg in my case is:

[image: Screen Shot 2019-06-12 at 14.37.37.png]
but [(1.6 * 10^-19)^2 * (10^-18)] / [6*V*K_B*T] is equal to 7.20677e-12
considering the conversion of MSD of dipole moments from (enm)^2 to (em)^2
so it would be really helpful to add a hint in the documentation or the
code about that.
Finally, as far as I understood the reported sigma value in the output of
dsp.xvg should be multiplied by 10^-12 manually.
It took sometime for me to understand what is going on in the output :-)
Please correct me if I'm wrong or missed something in these comments.

Best regards,

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