09.12.2015 20:57, Michał Wojciechowski wrote:
Currently I’m performing calculations for a chromium magnetic wheel  - 
Cr_8F_8(O_2CH)_16.
J = (E_FM - E_AFM)/36.
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.
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
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 started 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

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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