Dear Tone Thank you. It was very helpful. Regards David Foster
Ph.D. Student of Chemistry -------------------------------------------- On Wed, 5/28/14, Tone Kokalj <tone.kokalj at ijs.si> wrote: Subject: Re: [Pw_forum] ibrav7 doesn't show the structure of BaNi2As2 correctly To: pw_forum at pwscf.org Date: Wednesday, May 28, 2014, 1:25 PM On Wed, 2014-05-28 at 10:43 -0700, David Foster wrote: >? Dear Prof. Kokalj > > Maybe this question bored you, but it is important for me. Sorry for any inconvenience. > > Would you please give me more information that how to recognize the difference in the lattice definition. > If I am right in both softwares (QE and MS) A=B<C. > > So, how did you recognize the difference? Actually I didn't (at least initially). But from experience I know that such kinds of problems are typically due to mismatches in lattice definitions. Your reference to A=B<C pertains to conventional tetragonal-body-centered cell. This typically implies that conventional lattice vectors are V1=(a,0,0) V2=(0,b,0) V3=(0,0,c) But then there are multiple choices how to choose primitive vectors. The QE definition is (see INPUT_PW.txt): v1=(a/2)(1,-1,c/a)? v2=(a/2)(1,1,c/a) v3=(a/2)(-1,-1,c/a) but it can equally well be this (1st and 3rd vectors swapped): v1=(a/2)(-1,-1,c/a) v2=(a/2)(1,1,c/a) v3=(a/2)(1,-1,c/a) or any other possibility.? To see what effect this have when the coordinates are specified in fractions of lattice vectors (i.e. crystal coordinates), consider these two possibilities (patch appropriately your input file): &system ? ???ibrav=0,? celldm(1)=7.83745, ... CELL_PARAMETERS ? 0.5 -0.5 1.400757 ? 0.5? 0.5 1.400757 -0.5 -0.5 1.400757 ATOMIC_POSITIONS crystal ? Ba? ? ???0.00000???0.00000???0.00000? ? As? ? ???0.34710???0.34710???0.00000? ? As? ? ???0.65290???0.65290???0.00000? ? Ni? ? ???0.75000???0.25000???0.50000? ? Ni? ? ???0.25000???0.75000???0.50000? versus: &system ? ???ibrav=0,? celldm(1)=7.83745, ... CELL_PARAMETERS -0.5 -0.5 1.400757 ? 0.5? 0.5 1.400757 ? 0.5 -0.5 1.400757 ATOMIC_POSITIONS crystal ? Ba? ? ???0.00000???0.00000???0.00000? ? As? ? ???0.34710???0.34710???0.00000? ? As? ? ???0.65290???0.65290???0.00000? ? Ni? ? ???0.75000???0.25000???0.50000? ? Ni? ? ???0.25000???0.75000???0.50000? The second version gives correct structure, but the first version not. Regards, Tone PS: David, please just call me "Tone" w/o any "prof." prefix, which I am not. -- Anton Kokalj J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia (tel: +386-1-477-3523 // fax:+386-1-477-3822) Please, if possible, avoid sending me Word or PowerPoint attachments. See:? http://www.gnu.org/philosophy/no-word-attachments.html _______________________________________________ Pw_forum mailing list Pw_forum at pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
