[CP2K-user] [CP2K:11946] Ionic crystals with GFN-xTB

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

Hi

we also found that xTB is rather unstable for some systems/atom types.
We think this is mainly due the 3rd order Coulomb term and the
value of gamma (its proportionality factor).
Currently, I don't have an easy solution ready. In your case I would
start with some test calculations on the simple molecules, e.g. CaF2.
You can then try to re-parameterize the atoms (or just the metal?).
You can add the parameters to the input file (see examples in the regtests)
for easy changes.

regards

Juerg
--------------------------------------------------------------
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: "mpol" 
Sent by: cp... at googlegroups.com
Date: 07/04/2019 10:57AM
Subject: [CP2K:11946] Ionic crystals with GFN-xTB

Dear CP2k developers and users,

Have anyone encountered a problem with GFN-xTB when modeling ionic crystals? If I set

CHECK_ATOMIC_CHARGES .TRUE.

When performing CELL_OPT of a CaF_2 supercell, the program stops with the following warning:

*** WARNING in xtb_matrices.F:1088 :: Atomic charges outside chemical   ***
 *** range were detected. Switch-off CHECK_ATOMIC_CHARGES keyword in the ***
 *** &xTB section if you want to force to continue the calculation.      ***

Setting CHECK_ATOMIC_CHARGES .FALSE. makes the calculation divergent. As I get it, the charges on Ca and F become more and more unphysical in every SCF procedure, and, concomitantly, the total energy becomes lower and lower. I have attached the input and output of the divergent calculation to this message.

Could anyone give a hint on what to do in this situation? I am interested in MD of solid-liquid interfaces with ionic crystals. GFN-xTB seems the best choice.

With best regards,
Mikhail  
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[attachment "test1.inp" removed by Jürg Hutter/at/UZH]
[attachment "opt.cif" removed by Jürg Hutter/at/UZH]
[attachment "opt.xyz" removed by Jürg Hutter/at/UZH]
[attachment "test1.out" removed by Jürg Hutter/at/UZH]