[CP2K:9944] Problematic DFTB geometry optimization

hut... at chem.uzh.ch hut... at chem.uzh.ch
Fri Feb 2 10:47:25 UTC 2018


CP2K uses for DFTB a minimum image convention (MIC). This
causes interactions to be dropped for very small unit cells.
MIC is not used for k-point calculations. So by using the
k-point code with the gamma-point only you should be able
the reproduce the energies also for very small cells.

I would start with isolated systems (molecules) to be sure
that all the integrals are correctly calculated.

best regards

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: Maxime Van den Bossche 
Sent by: cp... at googlegroups.com
Date: 02/02/2018 12:19AM
Subject: Re: [CP2K:9944] Problematic DFTB geometry optimization

OK, I've noticed that the repulsive energy
of the initial structure in the above example
is different in CP2K and DFTB (5.2533030486
and 5.3189364428 Ha, respectively), so I've
now looked at a simpler structure (linear 
TiO2 chains) to see where that difference
is coming from.

I've appended a slide showing the results
for various chain structures, which seem to
indicate that certain pairs are missing from the
repulsive energy sum in CP2K. Is this a bug
in the code, or must this be handled through
the input somehow? I've also attached the 
CP2K in- and output files for the (N=1, L=5) 
case of the overview.



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[attachment "overview.pdf" removed by Jürg Hutter/at/UZH]
[attachment "tio2_chain.zip" removed by Jürg Hutter/at/UZH]

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