[CP2K:5794] Problem with DAVIDSON algorithm

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

Hi

I cannot comment on the problems you see for the Davidson
diagonalization combined with the other options.
However, if there are problems with the standard diagonalization
option, switching to Davidson will not help.
Davidson was intended as an alternative for large systems. It was
hoped that it is faster than direct diagonalization. 

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: cp... at googlegroups.com
From: Michael B 
Sent by: cp... at googlegroups.com
Date: 10/29/2014 05:15PM
Subject: [CP2K:5794] Problem with DAVIDSON algorithm

Hi,

I am currently running calculations on Ni(OH)2 and related Co(OH)2 surfaces. Following a previously tested method I fix the spin of the system to a constant value rather than converging it. Since I ran into convergence problems for some of the systems I switched from the STANDARD diagonalisation scheme to the DAVIDSON algorithm. This resulted in a strange behaviour of the calculations:

Problem I)

Despite explicitly fixing the spin to a constant value the total spin is no longer constant but starts to change during the calculation when using a DAVIDSON algorithm. I.e. when fixing the multiplicity to 8 (7 unpaired electrons) I obtained after several geometry steps 10 unpaired electrons. (complete output file is attached as results.log)

When using the same input parameters apart from an increased smearing of 0.3 eV (~3600 K) and a drastically reduced number of additional MOs (see 2nd problem) in combination with the STANDARD algorithm the spin remains constant. The following commands were used to fix the spin (complete input attached as cp2k_input.inp):

---quote---
[...]
UKS TRUE
MULTIPLICITY 8
RELAX_MULTIPLICITY -1

[...]

FIXED_MAGNETIC_MOMENT 7

[...]
---quote---

Is this a planned behaviour and if so is there a possibility to fix the spin in combination with a DAVIDSON algorithm?

Problem II)

Using the DAVIDSON algorithm in combination with "SCF_GUESS ATOMIC" seems to result in a very strange convergence behaviour. Approximately 5 times the number of additional MOs are required (in the present case an increase from 20 ADDED_MOs to 100 ADDED_MOs was required) in order to avoid occupying all orbitals. Independent of whether one provides the required number of additional MOs or not each(!) SCF WAVEFUNCTION OPTIMIZATION step requires only 2 SCF steps to converge.

The obtained total energies for the single steps seem to vary randomly but the final total energy obtained for each geometry step remains after some changes during the first three steps constant. The obtained energies are off by approximately 20 Ha compared to what be expected based on previous results using a STANDRAD diagonalisation algorithm. The input strucutre was already reasonably well converged.

This problem is independent of the choice of system and the behaviour can reproducibly be switched on by the above combination of parameters. The relevant input and output files are attached to this message.

Interestingly replacing "SCF_GUESS ATOMIC" by "SCF_GUESS RANDOM" seems to cure this problem, i.e. the SCF cycle behaves normally and the obtained total energies are reasonably close to what one could expect based on previous calculations.

Is this behaviour due to a bug or simply due to an unlucky combination of parameters?

All the best

Michael
  
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[attachment "results.log.zip" removed by Jürg Hutter/at/UZH]
[attachment "cp2k_input.inp" removed by Jürg Hutter/at/UZH]