Dear Dr. Cococcioni, Thanks a lot for the reply. It is very clear. I appreciate it.
On Sun, Dec 2, 2012 at 12:25 PM, Matteo Cococcioni <matteo at umn.edu> wrote: > Dear Peng, > > I'm not entirely sure about what you mean by "site symmetry". > Anyway, if two atomic positions are not equivalent by (point group) > symmetry, then the U will likely be different and should be recomputed > for each of them. This is the case of Fayalite. > Some times you can avoid recomputing the U if the only difference > between the atomic sites is the sign of magnetization. This is the > case of FeO or other transition-metal oxides with the same > stoiciometry. In these systems you have two TM atoms in the unit cell > one with spin up the other with spin down (but the same absolute > magnetization: in fact the material is AF). > If you are not sure about what to do, a good way to decide whether you > need to recompute U or not is to look at the atomic occupations > printed by the code (which are, in fact symmetrized). If two atoms > have different occupations (the difference has to be larger than > possible numerical noise, usually affecting occupations at the 4th > decimal point) and their occupations cannot be obtained one from the > other just interchanging majority with minority spins, then you need > to recompute U. > > Regards, > > Matteo > > On Sun, Dec 2, 2012 at 11:02 AM, Peng Chen <pchen at ion.chem.utk.edu> wrote: > > Dear All, > > > > In the calculations of U, I remember that I got some advice from the > forum > > that the equivalence of the ions is determined by space group symmetry > not > > site symmetry. E.g AB2O3, B ions has 2 different site symmetries (B(1) > > B(2)). We should only run the calculation on perturbing B ions. But from > > Dr. Matteo Cococcioni's paper (PRB 71, 035105 (2005)), both Fe1 and Fe2 > of > > fayalite are perturbed and have different U values. I think Fe1 and Fe2 > are > > different in site symmetry. So I am just curious which is the best way > to > > do the same kind of calculations. > > > > -- > > Best Regards. > > Peng > > > > _______________________________________________ > > Pw_forum mailing list > > Pw_forum at pwscf.org > > http://pwscf.org/mailman/listinfo/pw_forum > > > > -- > Matteo Cococcioni > Department of Chemical Engineering and Materials Science, > University of Minnesota > 421 Washington Av. SE > Minneapolis, MN 55455 > Tel. +1 612 624 9056 Fax +1 612 626 7246 > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- Best Regards. Peng -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121202/ed2f07d4/attachment-0001.html