[CP2K-user] [CP2K:12218] CUTOFF and REL_CUTOFF

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

Hi

1) the cutoff depends on the pseudopotential, F will need much
   higher cutoff than Se.
2) Defaults are okay (logarithmic)
3) For high cutoffs, I usually use 5 or 6 grids

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: "Pierre-André Cazade" 
Sent by: cp... at googlegroups.com
Date: 09/12/2019 03:24PM
Subject: [CP2K:12218] CUTOFF and REL_CUTOFF

Dear CP2K users,

Following the tutorial to tune the CUTOFF and the REL_CUTOFF for two of my systems, I find that quite large value of the CUTOFF  (700 Ry for beta glycine and 900Ry for quercetin) are necessary to achieve a decent level of precision (about 1.e-6). I am a bit surprised considering my systems are made from C, N, O, H. On top of that, for beta glycine, the last grid is not used that much, unlike what is recommended in the tutorial. Therefore, I have a few questions:

1/ Are these large cutoffs normal, even for small atoms? Is the cutoff more dependent on the crystal structure than the atom type?
2/ Is it normal to have still a large number of gaussians distributed on the first grid? Should I always aim for having a larger number of gaussians on the coarsest grid than on the thinnest?
3/ How do one decide on the number of grids? Is 4 kind of a magic number or should one aim to tune this as well? How does it affect accuracy/performance?

I attached the input file I used to generate the series of CUTOFF and REL_CUTOFF for both systems as well as the results I obtained.

Thank you for your help.

Best regards,
Pierre    
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[attachment "quercetin_cutoff.inp" removed by Jürg Hutter/at/UZH]
[attachment "quercetin_cutoff.dat" removed by Jürg Hutter/at/UZH]
[attachment "bglycine_cutoff.dat" removed by Jürg Hutter/at/UZH]
[attachment "bglycine_cutoff.inp" removed by Jürg Hutter/at/UZH]