[CP2K-user] [CP2K:15578] Poor force convergence wrt basis set size

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

Hi

my guess (no proof available) would be that your specific system
with only S-S bonds is at the edge of the MOLOPT optimisation space.
The different variations (SR vs. orig) have been optimized for
energy and might be comparably sub-optimal for your system.

The set of S containing molecules used in the optimization is

Al2S3
CS2
H2SO4
S2
S5
SF2
HSSH
SF4
SF6

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: cp... at googlegroups.com
From: "Arthur France-Lanord" 
Sent by: cp... at googlegroups.com
Date: 06/16/2021 11:47AM
Subject: Re: [CP2K:15578] Poor force convergence wrt basis set size

Hi, 

Thank you for the suggestion. This contributed to reducing the noise on the forces, and MAE's are now ~ 30% smaller. However, I still observe almost similar performances for MOLOPT basis sets (from DZVP-MOLOPT-SR to TZV2P-MOLOPT, vs. TZV2PX-MOLOPT). In fact, the MAE is even slightly smaller for the smallest, short-range version of DZVP-MOLOPT. Could that be a symptom of over-completeness of basis sets including diffuse functions for this system? 

best, 
Arthur
Le mer. 16 juin 2021 à 10:56, <hut... at chem.uzh.ch> a écrit :
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
 ---------------------------------------------------------------
 
 -----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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 [attachment "cp2k.inp" removed by Jürg Hutter/at/UZH]
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