From tajkhors {*at*} mbp-sgi7.inet.dkfz-heidelberg.de Thu Jun 4 10:50:22 1998 Received: from mbp-sgi7.inet.dkfz-heidelberg.de (mbp-sgi7.inet.dkfz-heidelberg.de [193.174.59.125]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with SMTP id KAA03750 Thu, 4 Jun 1998 10:50:19 -0400 (EDT) Received: by mbp-sgi7.inet.dkfz-heidelberg.de (951211.SGI.8.6.12.PATCH1502/940406.SGI.AUTO) for chemistry "-at-" www.ccl.net id XAA28144; Thu, 4 Jun 1998 23:50:49 GMT From: "Emadeddin Tajkhorshid" Message-Id: <9806041650.ZM28142 #at# mbp-sgi7.inet.dkfz-heidelberg.de> Date: Thu, 4 Jun 1998 16:50:37 -0700 Reply-To: E.Tajkhorshid # - at - # DKFZ-Heidelberg.de X-Mailer: Z-Mail (3.2.0 26oct94 MediaMail) To: chemistry ^%at%^ www.ccl.net (Computational Chemistry List) Subject: Frequencies calculated at different levels of theory Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Dear Colleagues I have a question regarding the frequencies calculated at different levels of theory for the same molcule. Can we decide on the basis of the closeness of the frequencies obtaiened at one level to judge about the accuracy of the geometrical parameters calculated in that model? In the other words, do the numbers calculated for the frequencies depend only on the geometry, or there are other things which may influence the shape of the potential surface around the minimum and which may significantly differ from a level to another one. For example, we have calculated the geometry and vibrational frequencies of molecule A using two models, M1 and M2. The bond distances obtained from M1 and M2 are different. Can we compare the calculated frequencies to the experimental ones and say: because the vibrational frequencies of method M1 are closer to the experimental values, the geometrical parameters (in this case bond distances) are also more accurately predicted by the method. Thanx in advance -- Emad ********************************************************************* E. Tajkhorshid German Cancer Research Center; DKFZ Tel: +49 6221 42 2340 Dept. Molecular Biophysics (H0200) FAX: +49 6221 42 2333 P.O.Box 101949 69009 Heidelberg, Germany Email: E.Tajkhorshid(+ at +)DKFZ-Heidelberg.de ********************************************************************* * "Never express yourself more clearly than you think." -Niels Bohr * *********************************************************************