[Wien] Issue with different convergence results and QTL-B warnings

[Michał Wojciechowski]

- The execution is always the same. I used the -in1new switch on a copy of the case directory to determine the correct energy parameters. For the proper calculations I manually changed the energy parameters in case.in1c
- All the in-files are the same (except for the carbon part). So are the struct files
- I did not perform relaxation. I'm trying to stick to the original structure of the molecule.
- I use RKM=2.0 because the calculations are 3 times faster than for RKM=3.0 and it turns out that there is no significant difference between results (energy, J, MMI, gaps, ...) for RKM=2.0 and 3.0. Also changing RMT or k-sampling is unimportant (although for smaller RMT magnetic moments for Cr decrease about 0.2 Bohr magnetons). However this is based on my previous experience with PBE functional for these structures and it might not be true for B3LYP. The reason I use these RMT-s is because I wanted them to be the same as in Acta Phys. Pol. A. 127, 407 (2015) and Phys. Rev. B 73, 184431 (2006).
- As for the magnetic moments they are almost constant and definitely hold their orientation. The same goes for partial charges - in both approaches they are the same.
- Offtop: the relation J = (E_FM - E_AFM)/36 for Cr8 is obtained from a general Ising-like magnetic Hamiltonian:
H=sum(J*S_{i}*S_{i+1})
where S are spins of Cr ions, S=+/- 3/2. For 8 Cr this gives 8 interactions between neighboring ions and for AFM configuration
H=J * 8 * - 3/2 * 3/2=-18J=E_AFM
and for FM configuration
H=J * 8 * 3/2 *3/2=18J=E_FM
If we take the difference we get
E_FM-E_AFM=18J- -18J=18J+18J=36J


Best Regards
Michał Wojciechowski
PHD student at Institute of Physics
Department of Physics and Astronomy
University of Zielona Góra, Poland


----- Oryginalna wiadomość -----
Od: "Lyudmila Dobysheva" <lyuka17 at mail.ru>
Do: "A Mailing list for WIEN2k users" <wien at zeus.theochem.tuwien.ac.at>
Wysłane: czwartek, 10 grudzień 2015 12:02:08
Temat: Re: [Wien] Issue with different convergence results and QTL-B	warnings

I am not an expert in B3LYP, so I am writing about only general 
considerations.
The reason may be
1) different execution. For example, you have made, by accident, for the 
final calculation in first case -in1new, in second - usual, without this 
option. Check the executions in dayfile's, :log's, and everywhere where 
this info can be found. And check all parameters. Compare the in-files 
in the whole saved directories.
Though system looks rather symmetric, there are 5 nonequivalent Cr 
atoms. Had you done force relaxation? Is struct files identical in both 
cases? in all four cases?
2) Maybe some parameter doesn't reach convergence, so small variations 
in calculation scheme (starting electron density) gives different 
results. Under suspicion, imho, RKM = 2.0 (as far as I remember, the 
recommendation for H-containing systems is RKM=3), very different RMT
2.40 and 0.83 Bohr for Cr and H, single k point.
3) maybe this exotic scheme of potential gives you really two different 
points? Look in case.scf other parameters, especially magnetic moments 
of Cr's, especially FM states (the difference is largest. For AFM it 
looks for me as not different).
3A) maybe this is a peculiarity of B3LYP scheme, and its iterative 
procedure allows to fix solution in some points that are not real 
minimum. Maybe users with experience with B3LYP can add something about 
this.
3B) Maybe this different solutions are really different minimums due to 
different Cr atoms with differently distributed moments among them.

Offtop:
 > J = (E_FM - E_AFM)/36.
Why 36? There is another number of atoms?

Best wishes
Lyudmila Dobysheva
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