Dear Li Yan, dear Paolo, for me it is not clear what Le Yan exactly did (of course, I agree with you, Paolo!), thus, maybe some questions to Li Yan:
Which was the first grid, which you used to calculate the dispersion? Does the 6x6x6 mesh include also the points you calculated for checking the negavive values? I had a similar problem many years ago with a high-pressure phase of silicon, where an irregular softening appeared near Gamma, and I should have used a finer grid in z-direction, meaning instead of 4x4x4 something like 4x4x6 or 4x4x8, bcause of c/a=0.55. At least, it was not enough to go from a 2x2x2 to a 4x4x4 mesh. Thus, maybe you could optimize the choice of your grid with respect to the lattice constants... Best wishes, Katalin >> i use q2r.x to calculate the phonon dispersion curves for AgF. >> at 3GPa, there are many negative values for TA in the brillouin zone. >> then i just calculated one of these points, but i got a positive values. >> then i used 6*6*6 q mesh, no improvement is found. > > the Fourier interpolation performed by q2r.x yields the original phonon > frequencies at the q-points of the grid in q-space. If it doesn't, there is > something wrong somewhere in the procedure > > P. > -- > Paolo Giannozzi e-mail: giannozz at nest.sns.it > Scuola Normale Superiore Phone: +39/050-509876, Fax:-563513 > Piazza dei Cavalieri 7 I-56126 Pisa, Italy > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >
