[Pw_forum] DOS at Ef

[Gabriele Sclauzero]

Dear all,

Giovanni Cantele wrote:
>>> (neither for scf -  nor for nscf - calculations) or in the out files 
>>> of PP codes (dos.x and projwfc.x.).

the Fermi energy is printed only at the end of calculations for metals. In the case of 
insulators it is not defined. You can take any energy in the gap as reference value for 
the DOS plot.

>>> How can I find this value?
>> Using dos.x, you can obtain the Ef value by using its definition basing 
>> on number occupied electrons, but, in my opinion, this way is not such 
>> accurate.

For metals the Fermi level determined in this way is as accurate as in the previous scf or 
nscf calculation as long as you use the same kind and width of smearing.
Anyway, if you simply want to visualize the DOS you should use gaussians in order to avoid 
negative densities in the plot.

When dealing with insulators there's no Fermi level, but you can determined to a desired 
accuracy the top of the valence band, or, if you want, the energy of the HOMO.
To my knowledge the best way is to use the tetrahedron method (specify 
occupations='tetrahedra' in the nscf run): you don't need to specify any smearing and you 
can control the accuracy by comparing the DOS obtained with increasingly large k-points 
grids (in the nscf calculation).


HTH

GS

>  > 
> Can someone comment on that?
> I would say that, based on the fact that dos.x is run
> after an nscf calculation where a very dense grid in k space is used, this should be
> more accurate than other approaches.
> 
> giovanni
> 
> 
> --
> 
> Giovanni Cantele, PhD
> CNR-SPIN and Dipartimento di Scienze Fisiche
> Universita' di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
> Phone: +39 081 676910 - Fax:   +39 081 676346
> Skype contact: giocan74
> 
> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
> Web page: http://people.na.infn.it/~cantele
>                      http://www.nanomat.unina.it
> 
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
> 

-- 


o ------------------------------------------------ o
| Gabriele Sclauzero, PhD Student                  |
| c/o:   SISSA & CNR-INFM Democritos,              |
|        via Beirut 2-4, 34014 Trieste (Italy)     |
| email: sclauzer at sissa.it                         |
| phone: +39 040 3787 511                          |
| skype: gurlonotturno                             |
o ------------------------------------------------ o