Dr. Giannozzi, Thank you for your response. The attachment is my ph.x output file. I use nat_todo to allow only atom #25 to displace. The output file indicates that only representation 30 and 39 are to be done (the irreps). #39 has two modes, and #30 has one. In the output, there are three negative and three positive frequencies. Is there a way to distinguish which three are the meaningful ones?
Best, Kan-Ju On Mar 21, 2014, at 8:29 AM, Paolo Giannozzi <paolo.giannozzi at uniud.it> wrote: > 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 > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20140326/93cef9ce/attachment.html -------------- next part -------------- A non-text attachment was scrubbed... Name: ph.out Type: application/octet-stream Size: 35669 bytes Desc: not available Url : http://pwscf.org/pipermail/pw_forum/attachments/20140326/93cef9ce/attachment.obj -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20140326/93cef9ce/attachment-0001.html -------------- next part -------------- A non-text attachment was scrubbed... Name: smime.p7s Type: application/pkcs7-signature Size: 1575 bytes Desc: not available Url : http://pwscf.org/pipermail/pw_forum/attachments/20140326/93cef9ce/attachment.bin
