[Pw_forum] crystal or tpiba_b

[Giovanni Cantele]

On Mar 5, 2010, at 2:53 PM, Elie Moujaes wrote:

> Dear all,
>  
> I read that if we are trying to calculate the band structure, it is better to use {tpiba_b} in ATOMIC POSITIONS rather than {crystal}. Is the only difference related to the points that will be plotted at the end  because one is wrt to cartesian and the other relative to crystallographic axes?
>  
>  

I never used tpiba_b or crystal_b. Nevertheless, by reading the Doc/INPUT_PW.txt I understand that it is not a matter of tpiba vs crystal, but of tpiba_b/crystal_b vs tpiba/crystal. Using either tpiba or crystal, you must specify the full list of k-points you want to show in your band structure plot. On the contrary, the *_b options (tpiba_b/crystal_b) allow to specify, for each given line in the Brillouin zone, only the 1st and last point, together with the number of points along that line.

As an example, you can replace
K_POINTS {crystal}
5
0.0 0.0 0.0    1.0
0.1 0.0 0.0    1.0
0.2 0.0 0.0    1.0
0.3 0.0 0.0    1.0
0.4 0.0 0.0    1.0
0.5 0.0 0.0    1.0
with
K_POINTS {crystal_b}
2
0.0 0.0 0.0    5.0
0.5 0.0 0.0    5.0


The choice of either crystal_b or tpiba_b is instead driven by in which coordinate system (crystallographic axes or cartesian, respectively) you find easier to write the
components of the k-points you need.

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

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