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
