[Pw_forum] Problem with nbnd in clusters

[Cyrille Barreteau]

Stefano,

I did various checks on the smearing (mv,mp,fd..)
and the broadening. For nbnd=20 I systematically
find the same 'odd' result if diagonalization='david'
and I recover a 'reasonable' result if diagonalization='cg'
(similar to the one obtained with nbnd=12,25).
Let me also mention that the "odd" result gives a
lower energy than the "reasonable" one.

cyrille

-- 
==================================================================
Cyrille Barreteau  | phone : +33 (0)1 69 08 29 51
CEA Saclay         | fax   : +33 (0)1 69 08 84 46
DSM/DRECAM/SPCSI   | email cyrille.barreteau at cea.fr
Batiment 462       |
91191 Gif sur Yvette Cedex  FRANCE
          ~~~~~~~~~~~~~~~~~~~~~~~~
http://www-drecam.cea.fr/Images/Pisp/cbarreteau/cbarreteau_fr.html
================================================================== 



Stefano de Gironcoli wrote:

>methfessel-paxton smearing is  dangerous (because it is not 
>positive-defnite) when  k-point sampling is not sufficient.
>
>When dealing with a "fake metal" as your molecule where the Fermi energy 
>should fall in gap of the spectrum I think it is more advisable to use 
>simple gaussian or marzari-vanderbilt smearing. The spurious negative 
>weights of m-p smearing the occupation of levels just above the Fermi 
>energy can lock some spourios state that shouldn't be there ... If you 
>have many kpoints this (in my experience... Nicola has a different 
>opinion) is never a problem.
>
>In any case the  smearing contribution for a molecule should be  zero 
>... which is not the case in your  output ... particularly so  for the 
>problematic cases  with 12 or 25 bands..
>
>TEST>  grep -e TS -e ! Fe*.out
>Fe_dimer_gamma_nbnd12.scf.out:!    total energy              =  
>-121.76376536 Ry
>Fe_dimer_gamma_nbnd12.scf.out:     smearing contrib. (-TS)   =    
>-0.00157785 Ry
>Fe_dimer_gamma_nbnd20.scf.out:!    total energy              =  
>-121.76907297 Ry
>Fe_dimer_gamma_nbnd20.scf.out:     smearing contrib. (-TS)   =     
>0.00048313 Ry
>Fe_dimer_gamma_nbnd25.scf.out:!    total energy              =  
>-121.76376546 Ry
>Fe_dimer_gamma_nbnd25.scf.out:     smearing contrib. (-TS)   =    
>-0.00157856 Ry
>
>Does the problem (at least the one with 25 bands) disappears if you use 
>"m-v" of "gaussian" smearing ?
>I would expect so... otherwise there is still something else.
>hope it helps,
>stefano
>
>Cyrille Barreteau wrote:
>  
>
>>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
>>
>>- 
>>==================================================================
>>Cyrille Barreteau  | phone : +33 (0)1 69 08 29 51
>>CEA Saclay         | fax   : +33 (0)1 69 08 84 46
>>DSM/DRECAM/SPCSI   | email cyrille.barreteau at cea.fr
>>Batiment 462       |
>>91191 Gif sur Yvette Cedex  FRANCE
>>          ~~~~~~~~~~~~~~~~~~~~~~~~
>>http://www-drecam.cea.fr/spcsi/index.php
>>http://www-drecam.cea.fr/Images/Pisp/cbarreteau/cbarreteau_fr.html
>>http://www-drecam.cea.fr/Phocea/Membres/Cours/index.php
>>================================================================== 
>>
>>
>>
>>
>>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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>>>
>>>    
>>>      
>>>
>>-
>>
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