[CP2K-user] [CP2K:13675] Energy convergence failed on large surface system?

Thomas Kühne tku... at gmail.com
Wed Jul 29 14:19:39 UTC 2020

Dear jt Yang, 

the basis set convergence you observed is already very good! Increasing 
the cutoff values further, but don’t forget that other parameters such as 
EPS_SCF and EPS_DEFAULT may have a much bigger impact. 
In general, you may ask yourself if your target is to single out the PBE limit, 
or to do the most accurate calculation within given computational resources. 
In the case of the latter, available computer time is most likely better spend 
by simply increasing the level of theory beyond GGA-based DFT than 
painstakingly trying to improve upon an already converged basis. 


> Am 28.07.2020 um 08:23 schrieb jt Yang <jtyan... at gmail.com>:
> Hi,
> I got a energy converge problem on a surface system.
> - system: TiO2 slab with MeCN adsorbed at it, 192 atoms, vaccum layer 20 angs.
> - with `NGRIDS=4, REL_CUTOFF=80, CUTOFF=1200` and NLCC basis, as adviced by the post <https://groups.google.com/forum/#!topic/cp2k/GwdlTOVgBYc>, the convergence i got is e-5 a.u.
> - could I push it to e-6 a.u. with higher `NGRIDS` or `REL_CUTOFF`, is that make sense?
> - or for a system like this, it's not realistic to that high accuracy?
> here is my result:
> relcutoff cutoff E a.u. (PBE)
> 80 600 -4644.229268091786
> 80 700 -4644.229265371339
> 80 800 -4644.229242358915
> 80 900 -4644.229242904181
> 80 1000 -4644.229242703446
> 80 1100 -4644.229243509899
> 80 1200 -4644.229242879066
> Best wishes,
> jtYang
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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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