From owner-chemistry@ccl.net Tue Jul 8 11:19:00 2008 From: "Ol Ga eurisco1-.-pochta.ru" To: CCL Subject: CCL: Failure TS opt caused by methyl rotation Message-Id: <-37314-080708104454-7316-pim2JxRVHdT+yVuwgui01g[a]server.ccl.net> X-Original-From: "Ol Ga" Date: Tue, 8 Jul 2008 10:44:50 -0400 Sent to CCL by: "Ol Ga" [eurisco1 .. pochta.ru] Dear Zheng Xu ! I intend that correct route sections are Step 1. #p ub3lyp/6-31++g(d,p) pOpt(qst2,noeigen,ModRedun) # scf(xqc,vshift,tight,Maxcycle=512) and freeze some (possible all) H-atoms to forbid rotation CH3-groups. You need to find out numbers of H-atoms in Z-mat and type in the job file number_H-atom_1 F number_H-atom_2 F ................ Step 2. #p ub3lyp/6-31++g(d,p) opt(calcall,ts,noeigen,gdiis,tight) guess=always # scf(xqc,tight,Maxcycle=512) Possible a lot of trials is necessary to achieve a saddle point if it exists on the level of theory Sincerely Ol Ga ----- Original Message ----- > From: "Zheng Xu zjuxuzheng###hotmail.com" To: "Ga, Ol " Sent: Tuesday, July 08, 2008 6:19 AM Subject: CCL: Failure TS opt caused by methyl rotation > > > Sent to CCL by: "Zheng Xu" [zjuxuzheng|-|hotmail.com] > Dear CCLers, > > I'm trying to get the TS of dimethylsilylene (Me2Si) insertion into Si-Cl bond of SiH2FCl. > > I have tried many times with different opt keywords(gdiis,tight or verytight ), howerver alll attempt was a failure. From the plot of "total energy" vs. "optimization step number", an unregular energy perturbation aroused by the rotation of two methyl groups was detected. > > Howerver, when ths substrate was changed from SiH2FCl to SiH3Cl, a right TS can be obtained. > Why? What should I do, is there anyone have good suggestion? > > --------------------------------------------------------------------------- > #p rb3lyp/6-31++g(d,p) opt(calcfc,ts,noeigen,gdiis) freq pop(regular,nbo) test > --------------------------------------------------------------------------- >