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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20130301/5156ceec/attachment.htm>