Energy convergence failed on large surface system?

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jt Yang

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Jul 28, 2020, 2:23:41 AM7/28/20
to cp...@googlegroups.com
Hi CP2K group,

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, 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

Thomas Kühne

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Jul 29, 2020, 10:19:45 AM7/29/20
to 'Dorothea Golze' via cp2k
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. 

Cheers, 
Thomas

Am 28.07.2020 um 08:23 schrieb jt Yang <jtyan...@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, 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
Germany

jt Yang

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Jul 29, 2020, 1:06:55 PM7/29/20
to cp2k
Hi Thomas,

Thanks for the reply,

To more clarify, I post this question because there may be more functional will be tested and I want a relatively high accuracy(e-6 a.u. say) at the same time, so a big safe cutoff is needed.

I'll try EPS_SCF and EPS_DEFAULT later, thank you!

Best wishes,
jtYang
To unsubscribe from this group and stop receiving emails from it, send an email to cp...@googlegroups.com.


==============================
Thomas D. Kühne
Dynamics of Condensed Matter
Chair of Theoretical Chemistry
University of Paderborn
Warburger Str. 100
D-33098 Paderborn
Germany

To unsubscribe from this group and stop receiving emails from it, send an email to cp...@googlegroups.com.


==============================
Thomas D. Kühne
Dynamics of Condensed Matter
Chair of Theoretical Chemistry
University of Paderborn
Warburger Str. 100
D-33098 Paderborn
Germany

To unsubscribe from this group and stop receiving emails from it, send an email to cp...@googlegroups.com.
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