Problem in the preconditioner when using UKS

[Daniele Ongari]

Dear CP2K developers, 
I want to report a serious problem with the preconditioner when computing 
the energy of Fe-MOF-74 with UKS settings.
Long story short the energy goes down, it is close to convergence but then, 
after recomputing the preconditioner in the outer step it starts to 
diverge: see the image.

[image: image.png] <about:invalid#zClosurez>




























Now, I attached the input and the output, but I already tried very 
different settings:
-smearing
-diagonalization without smearing
-different BS
-UKS false (converged, but to a higher energy, forcing the closed shell)
- starting magnetization on metals
- CG minimizer
- lower multiplicity
- 2x and 3x replicated unit cell in the shortest dimension
- lowering ENERGY_GAP to 0.001
These calculation ALL failed (I made 16 attempts in total, changing 
settings!).

And at the end the only one working (the 17th attempt, ironically the 
unlucky number for Italians!) was to use CG minimizer with *no outer SCF*, 
hence not recomputing the preconditioner. It converged after ~600 inner 
steps, to:

 HOMO - LUMO gap [eV] :    1.917671
 HOMO - LUMO gap [eV] :    0.235602

 ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):            
-1170.045288008604075

Please let me know what was the problem, if it is a known issue of the 
preconditioner and how to circumvent it: for the moment I'm using no outer 
steps to have a robust convergence, but I know that this may cause the 
convergence to a local miniimum!

Thanks a lot!

Daniele 
PhD candidate, LSMO, EPFL Sion













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