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

[Michał Wojciechowski]

Dear Wien2k users!
Currently I’m performing calculations for a chromium magnetic wheel - Cr_8F_8(O_2CH)_16. While I intend to get various quantities the primary one is magnetic interaction parameter J between chromium ions. To that end I require energies of two spin configurations - ferromagnetic (E_FM) and antiferromagnetic (E_AFM) - since J = (E_FM - E_AFM)/36.
The case file is attached. I’m using RKM = 2.0 (NMATMAX = 50 000, so RKM is unreduced), RMT = 2.40, 1.20, 1.24, 1.00 and 0.83 Bohr for Cr, F, O, C and H, respectively, single k point since it is a molecule. Remaining parameters are default or as suggested by the program. I use two approaches.
Approach 1.
I start with PBE functional from a command line with:
runsp_lapw -i 50 -ec 0.00001 -cc 0.001
The calculations converge nicely with no warnings or errors. I then change the XC functional to B3LYP (option 47 in case.in0 and additional case.ineece file) and run the command:
runsp_lapw -eece -i 50 -ec 0.00001 -cc 0.001
The calculations converge nicely with no errors but there is a single warning:
:WARN : QTL-B value eq.  11.12 in Band of energy  -2.28970  ATOM=   27  L=  0
Atom 27 is carbon. The case.in1 entry for this atom is
  0.30    3  0      (GLOBAL E-PARAMETER WITH n OTHER CHOICES, global APW/LAPW)
 0   -0.71      0.002 CONT 1
 0    0.30      0.000 CONT 1
 1    0.30      0.000 CONT 1
Using -in1new I was able to determine, that using parameter -1.70 instead of 0.30 resolves the issue. I then changed entries for all carbon atoms to
  0.30    3  0      (GLOBAL E-PARAMETER WITH n OTHER CHOICES, global APW/LAPW)
 0   -0.71      0.002 CONT 1
 0   -1.70      0.000 CONT 1
 1    0.30      0.000 CONT 1
and continued the calculations. This time I got no warnings and obtain results:
E_FM = -24370.92259156 Ry
E_AFM = -24370.92652933 Ry
J = 1.5 meV
Approach 2.
I starte with PBE functional and already modifie energy parameter in case.in1. After convergence is reached I continue with B3LYP functional. No warnings are present and I obtain the following results:
E_FM = -24370.91735838 Ry
E_AFM = -24370.92522898 Ry
J = 3.0 meV
So the issue is why are there such big differences? Which quantities should I check to determine the source of these discrepancies?
I am running Wien version 13.1 on a one, single processor, multi-core Intel Xeon machine with openSUSE 13.1 operating system. Programs were build with Intel compilers and math libraries (Intel Composer 2013 SP1) and OpenMPI 1.6.5.

Best Regards

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