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

Thu Dec 10 14:42:09 CET 2015

a) Interesting choice of RMTs, but probably not optimal. You should use 
setrmt as basis for your choice. It would reduce RMT(H) (0.6) and 
increase R(C) a bit, but still make Oxygen 15% larger than C. In 
particular the F-spheres are much too small at present. I'd use 2.0/1.6 
or 1.9/1.7 for Cr and F spheres.

RKMax=2.0 with your spheres is VERY small and I'd NOT trust any results 
with this setup. With my spheres you need RKMax 2.5-3.0.

b) I agree, for such molecular materials, our default E-parameters might 
not be optimal and problems for all the small spheres F, O and C may 
appear. Even WITHOUT QTL-B warnings, the E-parameter of F and O may not 
be optimal !
As mentioned many times on the mailinglist, the way to check this is 
looking at case.scf1 and case.scf2. It is not enough just to look at 
case.in1c, as these numbers will be changed automatically in lapw1:
0.3   --->  EF-(or+) 0.2
-0.71  0.002 ---> it tries a search, but for small spheres it probably 
will actually use -0.71 because it does not find E-top

You probably find in case.scf1 that the two C-s (l=0) E-parameter are 
very close to each other (using the default input)!

a) Locate the fermi energy !
b) locate the mean energies of C-2s (and O-2s and F-2s) by looking in 
case.scf2  (:EPL and :EPH)
c) change the FIRST line for l=0 of all the small atoms to this E-value 
in case.in1c (for C this might be -1.7 in your case). Leave the 0.30 
untouched, as this will be automatically adjusted according to EF. 
Repeat this for ALL "small" atoms (except for H).

---------------------
Otherwise:  compare the magnetic states of your calculations. I'm rather 
surprised that also the FM solutions are different, but it could well 
be. We know that all "orbital-dependent" potentials (like LDA+U or 
hybrid-DFT) depend a lot on the starting electronic structure.
Compare the :MMI and :QTL values.

If your calculations are ok, then the total energy is a good measure, 
which state is most favorable.

On 12/09/2015 05:57 PM, Michał Wojciechowski wrote:
> 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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>

-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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