Thanks Burak. I appreciate your suggestions and I will try. On Tue, Jul 10, 2012 at 11:11 AM, Burak Himmetoglu <himm0013 at umn.edu> wrote:
> Hi Peng, > > In my experience, the process of shifting the O atom to the origin is > recommended since it produces more stable results numerically, especially > in the second part of r.x where the program extrapolates to larger > supercells using the results from the starting supercell you have used. > However, if the crystal has already very small number of symmetries, then > you should be able to avoid this shifting. > > The first three entries in filepos are the lattice vectors in units of > alat (like the CELL_PARAMETERS when ibrav=0). The unit cell is expanded by > a factor of 10 in the tutorial. The length scale in filepos is not > necessary. That file is used only to compare the distances between pairs of > atoms and the scale does not really matter. It is generally better to scale > up only for numerical stability reasons. > > Best regards, > > Burak > > On Tue, Jul 10, 2012 at 10:03 AM, Peng Chen <pchen at ion.chem.utk.edu>wrote: > >> When O is perturbed in the case of NiO in tutorial, it >> is re-positioned and there are 2 different kinds of O (first with 1 atom, >> the second with 7 atoms). Then the kind with only one O is perturbed. In >> the tutorial, it reads "This is done to preserve the largest possible >> number of symmetries". Is this process necessary? Can we just run >> computation without re-position? In that case, there is only one kind of O >> with 8 atoms. >> >> In the position file "filepos", the scale of cell length is always 10, >> even if the scale is 7.9 in NiO and 5.42 in Fe. Shall we always use 10 in >> position file no matter what the real scale is? >> >> On Tue, Jul 10, 2012 at 9:37 AM, Burak Himmetoglu <himm0013 at umn.edu>wrote: >> >>> Hi Peng, >>> >>> r.x assigns the values of the response matrices only by considering the >>> distance between atoms and whether they have the same spin and type or not. >>> This information has to be given by the user in the positions file >>> "filepos" read by &input_mat. If B(1) and B(2) are different types >>> (e.g. crystallographically) you should perturb them separately, as you >>> outlined in the procedure, and make sure that ntyp=3 (type 1 is B(1), type >>> 2 is B(2) and type 3 is O) in the namelist &input_mat that goes into r.x >>> >>> Best regards, >>> >>> Burak >>> >>> >>> On Tue, Jul 10, 2012 at 1:45 AM, Stefano de Gironcoli <degironc at sissa.it >>> > wrote: >>> >>>> I don't know the details of r.x code but I think that, physically, >>>> what matters is the two atoms are crystallographically equivalent or not >>>> .therefore I think space group symmetry is the relevant one. >>>> >>>> stefano >>>> >>>> >>>> On 07/10/2012 05:54 AM, Peng Chen wrote: >>>> >>>> Dear All, >>>> >>>> In the calculation of U, how can we determine the equivalence of the ions, >>>> by site symmetry or space group symmetry? >>>> E.g ABO3, B ions has 2 different site symmetries (B(1) B(2)). Shall we run >>>> calculation on perturbing B(1) and B(2) ions or just a B ion? >>>> >>>> In order to find U in B ions, I tried to run calculation with perturbing >>>> just on B, and r.x gave some errors that it needs to read more data. >>>> So I guess it needs the perturbed data from other atoms. Shall I use the >>>> procedures listed below? >>>> 1. run scf calculation with Hubbard_U(i)= 1.d-20 >>>> 2. run scf with perturbing on an A ion >>>> 3. run scf with perturbing on a B(1) ion >>>> 4. run scf with perturbing on a B(2) ion >>>> 5. run scf with perturbing on an O ion >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>> _______________________________________________ >>>> Pw_forum mailing listPw_forum at >>>> pwscf.orghttp://www.democritos.it/mailman/listinfo/pw_forum >>>> >>>> >>>> >>>> >>>> _______________________________________________ >>>> Pw_forum mailing list >>>> Pw_forum at pwscf.org >>>> http://www.democritos.it/mailman/listinfo/pw_forum >>>> >>>> >>> >>> _______________________________________________ >>> Pw_forum mailing list >>> Pw_forum at pwscf.org >>> http://www.democritos.it/mailman/listinfo/pw_forum >>> >>> >> >> >> -- >> Best Regards. >> Peng >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://www.democritos.it/mailman/listinfo/pw_forum >> >> > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > > -- Best Regards. Peng -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20120710/8f7f608b/attachment.htm
