>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 <[email protected]> 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 > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum > -- 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: [email protected] Phone: +39 081 676910 Skype contact: giocan74 ResearcherID: http://www.researcherid.com/rid/A-1951-2009 Web page: http://people.na.infn.it/~cantele _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
