On Thu, 2014-12-18 at 19:29 +0000, Mutlu COLAKOGULLARI wrote: > Dear Carlo, Andrea and Paolo; > The taking responds and advices from people who has experienced makes > me happy. > As Paolo and Carlo also said, cif2qe.sh is not working properly, (at > least for this case). Therefore, I used the other codes for double cross > check: pymatgen and cif2cell. The conventional cell has 64 atoms whereas its > primitive has 32 atoms. > Pymatgen is very proper for POSCAR output because it takes symmetry > analysis depend on Curtarolo-Setyawan's paper > [http://arxiv.org/abs/1004.2974v1] (MCLC5 - it gives also gamma angle, for > this case)...so, it is not matching with QE's ibrav settings depend on cell > vectors. Cif2Cell code gives the exactly same CELL_PARAMETERS card with > Quantum-ESPRESSO's ibrav=-13...that is the reason why I chose Cif2Cell code. > Andrea, it was my fault. I had been complicated among space groups(2/m > for sg:12 and 2/C for sg:15) and Herman-Mauguin notations(2/m for space > groups 12-15). You said that ”Using ibrav=-13 it is not necessary to add > these atoms in the list of atoms inside the unit cell." Andrea, you mean that > could I decrease the number of atoms in primitive cell if they have > symmetrized by last 4 symmetry operations in this case? By this way, the cell > lost half of atoms inside which is good news for computational resources. > I think so. As far as I understand there are two possibilities: 1) You apply all the 8 symmetry operations and use ibrav=-12 (simple monoclinic) obtaining 64 atoms. 2) You apply only the first four symmetry operations and use ibrav=-13 (one base centered monoclinic). Note however that in this case you have to refer the positions to the base centered monoclinic axes, while the positions that you obtain applying the symmetry are still referred to the simple monoclinic cell. The base centered monoclinic cell has one half the number of atoms of the simple monoclinic cell.
In no cases however QE will find 8 symmetry operations. In the first case because fractional translations will be disabled (the cell is actually a supercell). In the second case because there are only 4. It is not a question of notations, the point group for the space group C2/c is C_2h (that has 4 operations), there is no way to obtain a larger point group. HTH, Andrea > With my best wishes, > Mutlu. > > ------------------------------------------Dr. Mutlu COLAKOGULLARITrakya > Universitesi Fen FakultesiFizik Bolumu22030 Merkez-EDİRNE > _______________________________________________ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum -- Andrea Dal Corso Tel. 0039-040-3787428 SISSA, Via Bonomea 265 Fax. 0039-040-3787249 I-34136 Trieste (Italy) e-mail: dalco...@sissa.it _______________________________________________ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum