Diffusion Coefficient

[Raghvender]

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

[Thomas Kühne]

Dear Raghvendar, 

without full input file and units it’s hard 

to give any potentially useful advise. 

Cheers, 

Thomas

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==============================

Thomas D. Kühne

Dynamics of Condensed Matter

Chair of Theoretical Chemistry

University of Paderborn

Warburger Str. 100

D-33098 Paderborn

Germany

tdku...@mail.upb.de

+49/(0)5251/60-5726

[Nicholas Winner]

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?