Dear Stefano, My point is to compute the so-called "acoustic contribution" to thermodynamical properties such as heat capacity or so. It is commonly used in empirical models calculations (such as Debye-Einstein models). Moreover, I am working with big structures, and I have some trouble obtaining good dispersion curves near Gamma, so I would like to extract information from the acoustic branches over the complete Brillouin zone. This is related to the point of calculating thermodynamic properties with only gamma frequencies, so that a model has to be set for the acoustic part ( because, as it goes to zero, it can create some singularities). I am not sure to be very clear myself, this is exploratory. To say it in a different way, experimentally we have information on optical frequencies (at gamma point) but not easily on what's below (except sound wave velocity but as I said before I have some trouble having a good curve at low q for acoustic modes ). The goal is to calculate the contribution of those frequencies on which we have no information by optical spectroscopy.
Thanks in any case for your idea of "following the eigenvectors", this is probably the better one. Is there an easy way to do it? (I think I know the answer). Best wishes, Merlin Quoting degironc <degironc at sissa.it>: > close to gamma the acoustic branches have linear dispersion. > Away from gamma one should follow the modes that are connected > to these three modes at gamma. If there is no symmetry these are just > the three lowest branches. If there is some symmetry they can cross > a few branches with different symmetry labels and should be possible > to follow the acoustic ones comparing the eigenvectors. > But I dont see any special meaning of acoustic modes far away from > gamma. > What are you looking for ? > > stefano > > meheut at impmc.jussieu.fr wrote: > >> Dear Drs, >> >> I would like to use pwscf to compute the acoustic branches only of the >> crystal. I already computed the complete phonon dispersion, but the >> acoustic branches are crossing with other modes. Do you think possible >> to disjoin the acoustic modes frequencies from the other modes? >> >> Best wishes. >> >> Merlin meheut >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://www.democritos.it/mailman/listinfo/pw_forum > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum
