[CP2K-user] Diffusion Coefficient

Nicholas Winner nwi... at berkeley.edu
Wed Apr 22 18:44:33 UTC 2020

This could be a problem with how you ran your simulation, but it could 
equally be a problem with your calculation/interpretation of diffusion 
coefficient. You'll need to provide more info. Consider these while you 
provide more info.

(1) Are you sure you are getting enough sampling? How is the ergodicity of 
this system? Perhaps look at (a) energy vs. simulation time, (b) your MSD 
plots, (c) the velocity autocorrelation function
(2) How is the the diffusion coefficient that you "want" acquired? Is it 
from simulation or experiment? If its from simulation, make sure every 
setting is the same and try to match it before you start customizing your 
input. If its from experiment, then a difference of that order is very 
understandable. Experimental diffusion coefficients can be very inaccurate 
depending on the nature of the system or the type of measurement, and even 
when the experiment is very carefully performed, it can still be different 
from theory.
(3) What sort of statistically sampling are you using to extract the 
diffusion coefficient? 

On Tuesday, April 21, 2020 at 1:58:43 PM UTC-7, Raghvender wrote:
> Hi everyone,
> I am trying to simulate TeO2 amorphous system at 1000K with 180 atoms (60 
> Te). So, the way I did was to generate a random configuration followed by 
> 5ps of the run at 300K. Then I did the same for 600K. After that I 
> increased the temperature to 1000K. 
> So, my problem is I have already simulated my system for 70ps but still, 
> the diffusion coefficient I am getting is of order of (10e-6). I want this 
> to be order of (10e-5). How can I get that?? 
> I am using RINGS code to calculate the diffusion coefficient.
> Thanks
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