[Pw_forum] Different band gap value from the 'relax' and 'nscf'calculation.

[#TAO JUNGUANG#]

Dear Giovanni;

Thanks a lot, you are very helpful and I think my problem should be due
to the reason as you explained. 
But one little thing should be mentioned is that I am using espresso-
2.1.5, so maybe something in this version should to be improved or I
have wrongly used it.

Regards.


Tao Junguang
 
Dear TAO JUNGUANG,
try to run one scf run at the optimized positions and immediatly after
the nscf.
I tried to do that with espresso-2.1.4 and got


  -47.5120 -47.4940 -24.1405 -24.1405 -23.9669 -23.9669 -23.9396
-23.9015
    -9.1803  -7.9537  -7.1715  -7.1715   2.9016   3.3425   3.7211
4.8903
     4.8903   6.1633   6.1633   6.7573   8.0547   8.3102   8.3102
8.7543
    10.5831  10.8792  11.1367  11.2196  11.2196  13.2185  13.3614
15.4703


So, 10.5831-8.7543=1.83 eV

Perhaps the pot and/or tho files were for some reason the wrong ones.

With previous releases I found some problem, due to the fact that
the potential after the nscf calculation seemed to change because 
overwritten.
This should have been corrected  in 2.1.4 or 2.1.5. In the Changelog of 
the cvs
version I find:

2005-05-27 14:52  giannozz

        * PW/: atomic_rho.f90, electrons.f90, potinit.f90, punch.f90:

        - do not set to zero the negative part of the charge density
          when starting from superpositions of atomic charges: it is
useless
        - print HOMO/top of the VB and LUMO/bottom of the CB when
available
        - always start from charge density and recalculate the
potential,
          also in a non-scf calculation
        - do not overwrite the charge density after a non-scf
calculation

So your problem could be due to overwritten charge density after
the nscf calculation.

Giovanni

-- 




Dr. Giovanni Cantele
Coherentia CNR-INFM and Dipartimento di Scienze Fisiche
Universita' di Napoli "Federico II"
Complesso Universitario di Monte S. Angelo - Ed. G
Via Cintia, I-80126, Napoli, Italy
Phone: +39 081 676910
Fax:   +39 081 676346
E-mail: Giovanni.Cantele at na.infn.it
Web: http://people.na.infn.it/~cantele

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