Dear all I was thinking again about keeping the space group symmetry fixed along a vc-relax calculation. Actually, I did not directly ask my main question...:-) Is there a way to put the above constraint which I am not aware of? Yours
Giuseppe ISM-CNR Italy Quoting Paolo Giannozzi <giannozz at democritos.it>: > > On Jul 10, 2011, at 12:10 , pascal boulet wrote: > >> Following Stefano's comment I need to provide ALL the atomic >> positions, >> which I did not do! I gave only the positions in the primitive unit >> cell (UC). > > what you call "primitive", I would call "irreducible" (like the > irreducible > segment of the Brillouin Zone) > >> But then, if I provide all the positions (I guess in the full UC) > > what you call "full", I would call "primitive" > >> why should QE fill the others? > > which others? > >> In addition, I did some calculations on Mg2Si (FCC, 12 atoms in the >> full UC) > > antifluorite structure? what you call "full" here, I would call > "conventional" > >> by providing only the 3 atoms of the primitive UC. QE found 48 >> symmetry >> elements, which is correct, and the optimized cell parameters >> seemed OK. >> So, still, is it wrong? > > no, because you provided all the needed atoms (3 in the unit cell of the > FCC lattice in the [anti]fluorite structure) > >> BTW, I also noticed something that looks strange to me. The >> coordinates >> reported by QE in the output are not those I give in the input: X >> and Y >> are the same but not Z which is scaled by c/a. > > nothing strange: atomic positions in input are in crystal coodinates: > >> ATOMIC_POSITIONS crystal > > atomic positions in output are in xyz coordinates, divided by a: > >> Cartesian axes >> >> site n. atom positions (alat units) > > P. > --- > Paolo Giannozzi, Dept of Chemistry&Physics&Environment, > Univ. Udine, via delle Scienze 208, 33100 Udine, Italy > Phone +39-0432-558216, fax +39-0432-558222 > > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >
