Dear Ali I just want to add something what Nicola, Giuseppe and Gabriele wrote. it is a good idea to reoptimize the structure after computing U. If you only need to optimize the lattice parameter (the atomic positions are fixed) this is easy: you just need to compute U for a series of different lattice parameter and then fit E vs V on a Murnaghan eq of state for example. If the relaxation of internal degrees of freedom is relevant there is a further level of consistency between U and the structure. In principle for each volume (or each pressure) you need to iterate the calculation of U with the internal relaxation. Hopefully U won't change much and an (average) U will work for all lattice parameters (as Nicola suggests) in your case. However we have recently found that a structurally consistent U has a finite effect, if not on energies, on their derivative wrt to V, i.e. pressure. see the paper PRB 79, 125124 (2009) for details.
regards, Matteo Nicola Marzari wrote: > Giuseppe Mattioli wrote: > >> I suggest you to reoptimize the lattice parameters. You could find quite >> different results with respect to the LDA or GGA results. >> > > > Also, as a matter of caution - do use a single U value in your > equation of state - ideally what you'd get from Cococcioni procedure > close to the minimum of the DFT+U equation of state. > > nicola > > --------------------------------------------------------------------- > Prof Nicola Marzari Department of Materials Science and Engineering > 13-5066 MIT 77 Massachusetts Avenue Cambridge MA 02139-4307 USA > tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/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 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
