[Pw_forum] Problem with nbnd in clusters

[Cyrille Barreteau]

Dear Paolo,

Maybe I found the second exception due to another very special
phase of the moon:-) What do I win in this case:-)

You will find at the following links:
the input file, the pseudo file and the three output
corresponding to nbnd=12,20,25 respectively.

http://www-drecam.cea.fr/spcsi/cbarreteau/tempo/Fe_dimer.scf.in
http://www-drecam.cea.fr/spcsi/cbarreteau/tempo/Fe.pw91.vdb.UPF
http://www-drecam.cea.fr/spcsi/cbarreteau/tempo/Fe_dimer_gamma_nbnd12.scf.out
http://www-drecam.cea.fr/spcsi/cbarreteau/tempo/Fe_dimer_gamma_nbnd20.scf.out
http://www-drecam.cea.fr/spcsi/cbarreteau/tempo/Fe_dimer_gamma_nbnd25.scf.out

thanks for having a look at this case.

   cyrille

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Paolo Giannozzi wrote:

>On Nov 20, 2007, at 15:55 , Cyrille Barreteau wrote:
>
>  
>
>>Does anyone has experience about the behaviour
>>of the various diagonalization schemes?
>>Which one is better, in which case?
>>    
>>
>
>the so-called conjugate-gradient diagonalization basically
>never fails; it uses less memory but it is much slower than
>the block Davidson algorithm. The latter is also quite
>robust but there is a tiny probability to end up in the wrong
>ground state. The only such case I know happens in some
>high-symmetry perovskites, if you start from superposition
>of atomic states, with occupied states only, and if the phase
>of the moon is close to 42. The problem disappears if you
>add a few more states, or if you start from random wavefunctions.
>I am quite surprised to hear that there is a case in which
>you get good results with 12 states and bad with 20.
>I wouldn't be surprised by the opposite. Could you please
>post one jobs showing the problem?
>
>Paolo
>---
>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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