[CP2K-user] [CP2K:15521] Poor force convergence wrt basis set size

[hut... at chem.uzh.ch]

Hi

I to be sure that you don't pick up basis set dependent numerical noise
I would suggest to use a more strict eps_default value, e.g. 1.E-14.

regards

Juerg Hutter
--------------------------------------------------------------
Juerg Hutter                         Phone : ++41 44 635 4491
Institut für Chemie C                FAX   : ++41 44 635 6838
Universität Zürich                   E-mail: hut... at chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland
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-----cp... at googlegroups.com wrote: -----
To: "cp2k" <cp... at googlegroups.com>
From: "Arthur France-Lanord" 
Sent by: cp... at googlegroups.com
Date: 06/06/2021 12:01PM
Subject: [CP2K:15521] Poor force convergence wrt basis set size

Hi, 

I'm currently testing atomic force convergence with respect to basis set size, for a crystalline polymorph of sulfur (an array of cyclic S8 molecules). I've tested both standard GTH basis sets (DZVP to QZV2P compared to QZV3P), and MOLOPT (DZVP-MOLOPT-SR to TZV2P-MOLOPT compared to TZV2PX-MOLOPT). I'm observing a slow or poor convergence behavior, which can be seen in these two plots (MAE : mean absolute error, MAPE : mean absolute percentage error, both only computed on the x components of the forces): 

GTH basis sets: 


MOLOPT basis sets (the TZV2P-MOLOPT/QZV3P panel is just shown here for comparison) : 


In particular, TZVP-MOLOPT performs slightly better than TZV2P-MOLOPT..? I'm using a high energy cutoff (2500 Ry and a REL_CUTOFF of 100 Ry), and a rather tight SCF convergence criterion (1.0e-7) with the OT method. Convergence in the SCF is achieved rather fast. 

Are these errors expected? I was trying to reproduce something similar from what ccan be seen in https://arxiv.org/pdf/1409.4527.pdf (figures 1 and 2), but didn't expect such high relative errors. The configuration I'm using is from a molecular dynamics run to obtain non-zero forces. I'm including a cp2k input file to reproduce the QZV3P calculation. 

many thanks, 
Arthur

  
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