[Pw_forum] Mis-printing of QE manual about primitive vectors of FCC and BCC?

[Giovanni Cantele]

>From the solid state physics textbook you can also learn that the choice of the primitive vectors is not unique. There might be different but equivalent
choices of the three vectors, all giving the same primitive cell volume. For example, in the case of FCC, with the origin fixed at a lattice site, the first neighbour
sites are 12, at positions (in a/2 units) : (+-1, +-1, 0) ; (+-1, 0, +-1) ; (0, +-1, +-1). Any three of these vectors is a good choice.

Same applies to BCC, where the number of first neighbours is six.

Giovanni

> On 23 Mar 2016, at 14:24, Tsung-Lung Li <quantum at mail.ncyu.edu.tw> wrote:
> 
> Dear QE users:
> 
> I am new to QE, and am trying to go through QE manual and tutorials to 
> learn QE.
> 
> On page "espresso-5.3.0/PW/Doc/INPUT_PW.html#idp28918944"
> I read the following about ibrav
> 
> ibrav = 2  cubic F (fcc)
>            v1 = (a/2)(-1,0,1),  v2 = (a/2)(0,1,1), v3 = (a/2)(-1,1,0)
> ibrav = 3  cubic I (bcc)
>            v1 = (a/2)(1,1,1),  v2 = (a/2)(-1,1,1),  v3 = (a/2)(-1,-1,1)
> 
> From my solid state physics textbook, I learned the primitive vectors
> 
> For FCC,  v1 = (a/2)(0,1,1),  v2 = (a/2)(1,0,1), v3 = (a/2)(1,1,0)
> For BCC,  v1 = (a/2)(-1,1,1),  v2 = (a/2)(1,-1,1), v3 = (a/2)(1,1,-1)
> 
> Why is there this difference?  Is it a mis-printing of QE manual?
> 
> If is is not a mis-printing of QE manual, could you please point me to 
> the right reference?
> 
> Thank you very much.
> 
> 
> Sincerely,
> Tsung-Lung Li
> 
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-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele