[Pw_forum] Problem with nbnd in clusters

[Cyrille Barreteau]

A final comment concerning this tricky problem.
I think I got the reason of my troubles.
I have two scf solutions:

1) one that (almost) satisfies the symmetry of the real dimer
and for which xy and x^2-y^2 eigenfunctions are degenerate.
However this solution has the bad idea of having an unfilled homo
state.

2) an other that do not satisfy the symmetry of the real dimer
(but of course satisfy the symmetry of the crystal) since a
rather large spitting of xy and x^2-y^2 is observed.

The second solution is the most stable for reasons related
to the so called Jahn-Teller effect. There is no true Jahn
Teller distorsion but the dissymetrization of xy and x^2-y^2
leads to a splitting of levels that decreases energy....
bad luck!

I guess this problem will disappear if I add spin-orbit coupling
since it will induce splittings and the (bad) chance to have
an unfilled homo state is smaller.

that's all folks.

   cyrille

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Cyrille Barreteau  | phone : +33 (0)1 69 08 29 51
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Paolo Giannozzi wrote:

>On Nov 21, 2007, at 8:54 , Cyrille Barreteau wrote:
>
>  
>
>>Maybe I found the second exception due to another very special
>>phase of the moon:-) What do I win in this case:-)
>>    
>>
>
>you won a nice discussion on DFT. Now you just have to write
>the paper :-)
>
>Actually your case is different from the one I was mentioning.
>In that particular case, the final state was "self-inconsistent",
>i.e. diagonalization of the final potential yielded different
>Kohn-Sham states, so it was a 100% guaranteed bug.
>In your case, it looks like there are two different, and very
>close in energy, self-consistent states
>
>P.
>---
>Paolo Giannozzi, Dept of Physics, University of Udine
>via delle Scienze 208, 33100 Udine, Italy
>Phone +39-0432-558216, fax +39-0432-558222
>
>
>
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