[Pw_forum] about DOS

[Eyvaz Isaev]

Hi,

> i have two questions:
> is "occupations=tetrahedra" right for obtaining DOS
> for a semiconductor  like TiO2?
Yes, it is. Nevertheless, I remember it was mentioned
in the forum (by Paolo?) that it may not  work for
noncubic structures. You can try the smearing
technique also, and you can compare is your DOS OK or
not.  

> because when i do an nscf calculation  without it
,my > DOS is  resonable according the band structure
,but 
> when i  use this occup-mode, DOS  is completely 
> different & i have not the gap too.
If I understood correctly, you did also nscf
calculations, but did not specify occupations. Did you
specify in this case a smearing (by default 
smearing="gaussian", and degauss=0.0 (Ry))? I do not
think that with degauss=0 you will obtain a correct
result. 

> second, when i do an nscf calc. then use dos.x , the
> integrated DOS is not  right in the gap,but when i 
> use dos.x right after  scf calculation ,i have 
> the right integrated DOS but it's obvious that the i
> have no DOS after the  gap.so what should i do to 
> have the right DOS and  integrated DOS ?
I am not sure that I understood correctly the first
part of this question, but for the last question an 
answer is that try a smearing with a nonzero degauss. 

If you are not sure on your results, send us your DOS
output files.
 
Bests,
Eyvaz.

  

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