Dear Xavier, you said that you choose the Ueff value to reproduce one property and then you use this Ueff value to predict the others. My question is can I choose Ueff to reproduce a structural property (such as the lattice constant or cell volume) and than use that value of Ueff to predict electronic properties?
On Fri, Mar 1, 2013 at 3:04 PM, Laurence Marks <L-marks at northwestern.edu>wrote: > If all you have are the atomic positions (and lattice constant) then the > only unbiased approach would be to calculate the U, see > http://www.wien2k.at/reg_user/textbooks/Constraint_U.pdf. > > N.B., the DFT+U method is variational for a fixed U, but I don't think it > is variational as a function(al) of U. > > On Fri, Mar 1, 2013 at 1:58 PM, Zsolt Rak <zsolt.rak at gmail.com> wrote: > >> Let's suppose that the atomic positions (and lattice constants) are the >> only information that I have. Is it physically justified to use LDA+U/GGA+U >> to optimize the volume? or to tune the U value to reproduce the >> experimental lattice constants? Also, is the DFT+U method based on the >> variational principle? >> >> On Fri, Mar 1, 2013 at 2:43 PM, Laurence Marks <L-marks at >> northwestern.edu>wrote: >> >>> You need more a-priori information than this, for instance the bulk >>> energy of related compounds for which a U is relevant. Tuning the U to >>> reproduce known data is not by itself spectacular science. >>> >>> On Fri, Mar 1, 2013 at 1:24 PM, Zsolt Rak <zsolt.rak at gmail.com> wrote: >>> >>>> I want to calculate the most accurate bulk energy and the a-priori >>>> information I have are the atomic positions. >>>> >>>> >>>> >>>> On Fri, Mar 1, 2013 at 1:59 PM, Laurence Marks < >>>> L-marks at northwestern.edu> wrote: >>>> >>>>> My two cents. Both LDA+U and GGA+U are wrong. That said, for f-/d- >>>>> systems they are often better than LDA/GGA for some properties. The >>>>> question you should ask yourself is what property are you trying to >>>>> measure/predict, and what a-priori information (reference state) do you >>>>> have that can be used? >>>>> >>>>> For instance, if I want to calculate a surface energy then I would >>>>> tune the U to give the most accurate bulk energy treating this as my >>>>> a-priori information; similarly if I wanted to calculate the elastic >>>>> behavior of a defect I would tune to the bulk elastic constants. In my >>>>> opinion this is the only justifiable approach. >>>>> >>>>> >>>>> On Fri, Mar 1, 2013 at 12:47 PM, Zsolt Rak <zsolt.rak at gmail.com>wrote: >>>>> >>>>>> Dear wien2k users, >>>>>> >>>>>> I am calculating the properties of several f-electron compounds. I >>>>>> would like to ask the users' opinion about the volume optimization in an >>>>>> f- >>>>>> or d-electron system: which way is better (or physically justified), with >>>>>> LDA/GGA or with LDA+U/GGA+U? In my opinion, the LDA+U/GGA+U techniques >>>>>> were >>>>>> developed to correct band energies of localized states, so there is no >>>>>> fundamental physical reason to use LDA+U/GGA+U methods for volume >>>>>> optimization. However, we observe a change in the lattice parameters when >>>>>> we go from LDA/GGA to LDA+U/GGA+U. Also, from a brief search of the >>>>>> literature we found that, in many cases, people tune the Hubbard-U >>>>>> parameter to reproduce the experimental lattice constants. >>>>>> I would appreciate further thoughts and insights into this issue. >>>>>> >>>>>> Thank you, >>>>>> Zs >>>>>> >>>>> >>>>> >>>>> >>>>> -- >>>>> Professor Laurence Marks >>>>> Department of Materials Science and Engineering >>>>> Northwestern University >>>>> www.numis.northwestern.edu 1-847-491-3996 >>>>> "Research is to see what everybody else has seen, and to think what >>>>> nobody else has thought" >>>>> Albert Szent-Gyorgi >>>>> >>>>> _______________________________________________ >>>>> Wien mailing list >>>>> Wien at zeus.theochem.tuwien.ac.at >>>>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >>>>> >>>>> >>>> >>> >>> >>> -- >>> Professor Laurence Marks >>> Department of Materials Science and Engineering >>> Northwestern University >>> www.numis.northwestern.edu 1-847-491-3996 >>> "Research is to see what everybody else has seen, and to think what >>> nobody else has thought" >>> Albert Szent-Gyorgi >>> >>> _______________________________________________ >>> Wien mailing list >>> Wien at zeus.theochem.tuwien.ac.at >>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >>> >>> >> > > > -- > Professor Laurence Marks > Department of Materials Science and Engineering > Northwestern University > www.numis.northwestern.edu 1-847-491-3996 > "Research is to see what everybody else has seen, and to think what nobody > else has thought" > Albert Szent-Gyorgi > > _______________________________________________ > Wien mailing list > Wien at zeus.theochem.tuwien.ac.at > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20130301/d152bb19/attachment.htm>