From owner-chemistry: at :ccl.net Thu Dec 20 05:04:01 2007 From: "Herbert Fruchtl herbert.fruchtl[a]st-andrews.ac.uk" To: CCL Subject: CCL:G: Problems finding TS Message-Id: <-35890-071220050102-15884-qg7wiMGDx65Y0TFj817OWw=-=server.ccl.net> X-Original-From: Herbert Fruchtl Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=ISO-8859-1; format=flowed Date: Thu, 20 Dec 2007 10:00:19 +0000 MIME-Version: 1.0 Sent to CCL by: Herbert Fruchtl [herbert.fruchtl],[st-andrews.ac.uk] What I usually do in this case: - Guess the length of the bond at the TS, or look for the maximum in a relaxed PES scan. - Optimize to a minimum with this bond frozen at this value. - Start TS search from this point. If possible, calculate a Hessian (with a smaller basis and a pure DFT functional like HCTH or BLYP) You have ModRedundant AND TS in your input. I don't know what you're freezing, but this won't give you a true TS. Also, if you are so far off that you need NoEigenTest, it's unlikely you find the correct TS. Herbert Debellis Anthony CE US anthony.debellis,,ciba.com wrote: > Sent to CCL by: Debellis Anthony CE US [anthony.debellisHello Oscar, > One possibility would be to locate the transition state with the methyl group removed, then add back the methyl to the resulting TS structure followed by a further TS optimization. > Anthony DeBellis > Ciba > > -----Original Message----- >> From: owner-chemistry^^ccl.net [mailto:owner-chemistry^^ccl.net] > Sent: Tuesday, December 18, 2007 12:05 PM > To: Debellis Anthony CE US > Subject: CCL:G: Problems finding TS > > > Sent to CCL by: Oscar Odio Chacón [odio---imre.oc.uh.cu] > > Hello, CCLers: > I´m trying to calculate the transition state of a radical addition reaction to an olefin using Gaussian 98. The problem arises because the output negative frequency does not correspond with vibrational motion of the bond formed in the product, but corresponds to a motion associated with a methyl group near the radical. So, what can I do? > Remove the methyl group? > In my opinion, this methyl group would have influence in the transition state energy. > The overall system contains 47 atoms, 415 basis functions, 707 primitive gaussians, 70 alpha electrons, 69 beta electrons. The command line was # > b3lyp/6-31g(d,p) opt=(modredundant, TS, noeigentest) freq. > Thanks in advance. > Oscar Odio > > > > > > -- > Lic. Oscar Odio Chacón > Laboratorio de Polímeros > IMRE > > > > "Al mundo nuevo corresponde la Universidad nueva" > UNIVERSIDAD DE LA HABANA > 280 aniversario > Participe en Universidad 2008 del 11 al 15 de febrero del 2008. > Palacio de Convenciones. La Habana. Cuba. > http://www.universidad2008.cuhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/spammers.txt > > > -> > > -- Herbert Fruchtl EaStCHEM Fellow School of Chemistry University of St Andrews