Dear Du,
duchl06 wrote: > dear pw users > could any one tell me which method is right? > 1)relax in GGA scheme, then use the Geometry do a GGA+U scf calculation > or > 2) relax in GGA+U scheme, got the Geometry, then a GGA+U scf calculation > The consistent way of proceeding is 2). consider however that structural minimization may suffer from the problem of having many local minima and typically one is interested in the lowest energy one. the two different results may therefore represent two different minima in your system landscape, reached because the history of the relaxation has been different for some random reasons. To check on that you might start a new GGA+U relaxation from the converged GGA geometry and see whether the system evolves toward the geometry you have found in the GGA+U relaxation, suggesting a real difference between the minima of the two methods, or remains in the neighborhood of the GGA minimum, suggesting that both minima are actually local ones for GGA+U. The ultimate decision on which minimum is better would then be taken on the basis of their energy .. paying attention to compare apples with apples, that is comparing GGA+U OR GGA energies among them and NEVER a GGA energy with a GGA+U one ... hope this helps, stefano > > I ask this question because i did a Geometry Optimization GGA scheme and > GGA+U (other parameters are almost the same), and i got a very pwdifferent > Geometry with the two method, why does this happen? > > best regards! > > Du > xiaguanying university > > ------------------------------------------------------------------------ > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >
