On Tue, 2014-03-18 at 16:57 +0000, Kan-Ju Lin wrote: > To facilitate the frequency calculation, I used nat_todo = 1 to only > allowing the helium to be displaced [...]
> My questions are: > 1. Why are there 3 additional frequencies? Shouldn?t there only be 3 > (omega 73~75) due to the DoF of one atom? nat_todo means that the calculation is performed only for irreducible representations containing a displacement of the chosen atoms(s). In the output of the phonon code, you should see how many irreps are used and their degeneracy. If there are 6 frequencies, there should be a total of 6 irreps. What you get as frequencies may not have any special physical meaning, with the exception of some special cases (e.g. molecule on a surface with well-separated modes) Paolo > 2. Why are the three additional frequencies negative? Shouldn?t there > be one negative frequency for the saddle point, and 2 positive > frequencies? and no negative frequency for the energy minimum? > > > Please let me know if I understand this incorrectly, or I am missing > some settings. > > > > > -- > Kan-Ju Lin, Postdoctoral Associate > MIT Materials Science and Engineering > Office 4-053 / kjlin at mit.edu > > > > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum -- Paolo Giannozzi, Dept. Chemistry&Physics&Environment, Univ. Udine, via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222
