AIMD of ACN doesn't converge after 100 ps

[Abdullah Bin Faheem]

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

[Thomas Kühne]

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. 

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

[Abdullah Bin Faheem]

Dear Thomas,

Thank you for suggestions. I will try them out

Regards,

Abdullah

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