[CP2K-user] [CP2K:13012] AIMD of ACN doesn't converge after 100 ps

Thomas Kühne tku... at gmail.com
Tue Mar 24 14:02:18 UTC 2020

Dear Abdullah Bin Faheem, 

there is nothing wrong. What you are observing is not due to incomplete equilibration, but 
rather a consequence, of incomplete SCF convergence. Beside time-step errors, which in 
your case may be non-negligible due to a discretized time-step of 1.0 fs,  the so-called 
„conserved quantity“ is in a numerical calculation only conserved at perfect SCF convergence. 
Hence, reducing the integration time-step and more importantly tightening the EPS_SCF 
should lead to a better conservation of the conserved quantity. However, in a numerical 
calculation the latter will never be perfectly conserved and it is up to you to decided what 
level gives you the best efficiency / accuracy compromise. 
I personally, would suggest 0.5-0.75fs for the time-step and 1e-7 - 1e-6 for EPS_SCF when 
using OT. I have commented on the differences between TD and OT wrt to EPS_SCF in an 
earlier posting. 


> Am 24.03.2020 um 14:03 schrieb Abdullah Bin Faheem <abdullahb... at gmail.com>:
> Hello everyone,
> I performed AIMD of 60 Acetonitrile molecules using cp2k 5.1.0. However, I noticed that "Cons Qty" keeps increasing and does not converge even after 100 ps. While on the other hand, the kinetic and potential energies reach equilibrium within 2-3 ps. Does this mean my system has not converged? Or is there something wrong with my input file?
> If so, any suggestions would be greatly appreciated for possible improvement/fixes. 
> I have attached the input and the energy output files, where the initial geometry for ACN was taking from classical MD.
> Thank you for your time
> Best Regards,
> Abdullah Bin Faheem
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Thomas D. Kühne
Dynamics of Condensed Matter
Chair of Theoretical Chemistry
University of Paderborn
Warburger Str. 100
D-33098 Paderborn
tdku... at mail.upb.de

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