From borkent@caos.kun.nl Wed Jul 10 04:13:07 1996 Received: from cammsg1.caos.kun.nl for borkent@caos.kun.nl by www.ccl.net (8.7.5/950822.1) id DAA14907; Wed, 10 Jul 1996 03:31:24 -0400 (EDT) Received: from cammsg5 (cammsg5.caos.kun.nl [131.174.88.5]) by cammsg1.caos.kun.nl (8.7.1/8.7.1) with SMTP id JAA00532 for ; Wed, 10 Jul 1996 09:31:16 +0200 (MDT) From: Hens Borkent Message-Id: <199607100731.JAA00532@cammsg1.caos.kun.nl> Subject: M: negative freq's. To: chemistry@www.ccl.net Date: Wed, 10 Jul 1996 09:31:15 +0200 (MDT) X-Mailer: ELM [version 2.4 PL25] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Dear CCL-ers, I mis-sent my reaction last week, but I think it is still relevant, so I repeat it here: In case you want to get rid of spurious negative frequencies (which is often not necessary for the conclusions you draw from a calculation) it helps if you visualize the movement involved (MOLDEN on unix machines, Re_view on PC's). I have had examples where these frequencies corresponded to small deviations from symmetry, and it helped to start with a perfectly symmetrical structure. E.g. I observed in an sp3-sp3 chain a motion corresponding to rotation around the central bond, with a negative frequency, after minimization. It disappeared after changing the dihedral angles from 179.5 to 179.9999. (and a full minimization of course, although you can do a step in between in which you fix the symmetry). Best regards, -- ***** J.H. (Hens) Borkent, CAOS/CAMM Center, *CAOS * P.O. Box 9010, 6500 GL Nijmegen, The Netherlands * / * Tel 0031 24 36 52137 Fax 0031 24 36 52977 * CAMM* e-mail: borkent@caos.kun.nl ***** http://www.caos.kun.nl/staff/borkent.html