[CP2K:9948] Problematic DFTB geometry optimization

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

Hi

the MIC is probably a left over from the original implementation.
I cannot remember why it was needed. If you think this should go
I can remove it in further versions. It is a one line change in the code.

If you want to use mixing, Broyden is probably more efficient.

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
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-----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 09:10PM
Subject: Re: [CP2K:9948] Problematic DFTB geometry optimization

OK, I see -- using a Gamma-point-only k-point grid indeed
gave the expected repulsive energy for the TiO2 molecule
as well as for the rutile structure (i.e. same as in DFTB+).
Using a  Gamma-point-only k-point grid also solved the 
original rutile geometry optimization issue, so the repulsive
interactions were indeed the culprit here. Would it be possible 
to document this behaviour more explicitly, e.g. in the manual?

Both for the isolated TiO2 molecule as for the rutile TiO2,
I needed to reduce the ALPHA value in the MIXING section 
to 0.11 or lower (with the DIRECT_P_MIXING scheme) to 
get the SCF to converge. Even then, 

I did some additional one-to-one comparison for an isolated 
TiO2 molecule. The electronic energy contributions (0th order 
Hamiltonian energy and the charge fluctuation energy),
as well as the charges and forces,  both with OT and (gamma-point) 
diagonalization, fully agree with DFTB+. This is the case,
provided that "orbital-resolved SCC" is turned off in DFTB+ 
(i.e. only one Hubbard value per element, that of the s-orbital in 
the SKF file, as mentioned previously). So the electronics
seem to be in order.

Regards,
Maxime  
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