From owner-chemistry:~at~:ccl.net Fri Apr 6 19:58:01 2007 From: "Abrash, Samuel sabrash^^^richmond.edu" To: CCL Subject: CCL:G: Method for Frequency Calculations Message-Id: <-33997-070406153550-20278-cXrf0+yYosJwJg32kxlvPQ^_^server.ccl.net> X-Original-From: "Abrash, Samuel" Content-class: urn:content-classes:message Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII" Date: Fri, 6 Apr 2007 12:57:15 -0400 MIME-Version: 1.0 Sent to CCL by: "Abrash, Samuel" [sabrash(-)richmond.edu] If you choose a DFT Method with a biggish basis set, you can get within a few % of literature values. People who do matrix isolation spectroscopy and commonly use Gaussian for vibrational spectrum calculations usually use B3LYP/6-311++G**. You can also get a sense of the accuracy by going to CCCBDB and going to scaling factors. The closer the scaling factor is to one for a combination of theory and basis set, the more accurate it is. HF performs worse than MP2 as far as absolute frequencies go, but tends to have frequency patterns that match experiment better. MP2 gives smaller scaling factors but can be unpredictable regarding whether frequencies are over or underestimated. Best regards, Sam Abrash Samuel A. Abrash Department of Chemistry University of Richmond Richmond, VA 23173 Phone: 804-289-8248 Fax: 804-287-1897 E-mail: sabrash#%#richmond.edu Web-page: http://oncampus.richmond.edu/~sabrash "Rabbi Yitzhak said: At the time God created the world and desired to reveal the depth of His being from out of the hidden, the light came > from the darkness and they were joined together. Because of this, out of darkness came the light and out of the hidden came the revealed and out of the good came evil and out of mercy came severe judgement, and everything is intertwined with everything else...the good inclination and the evil inclination, the right and the left." - The Zohar -----Original Message----- > From: owner-chemistry#%#ccl.net [mailto:owner-chemistry#%#ccl.net] Sent: Friday, April 06, 2007 11:15 AM To: Abrash, Samuel Subject: CCL: Method for Frequency Calculations Sent to CCL by: "Soren Eustis" [soren__jhu.edu] Disregarding any concerns with processor time and assuming extensive basis sets, what is generally accepted to be the most accurate method for frequency calculations of small (non-metallic) molecules? I have heard MP2 is not that great, but HF and DFT perform better? Am I on the right path here?http://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt