From owner-chemistry@ccl.net Thu Nov 27 03:37:01 2008 From: "=?ISO-8859-1?Q?=D6d=F6n?= Farkas farkas() chem.elte.hu" To: CCL Subject: CCL:G: Constraints? Message-Id: <-38184-081127031146-6271-Eukia90UMSS9johhVk2CcA^-^server.ccl.net> X-Original-From: =?ISO-8859-1?Q?=D6d=F6n?= Farkas Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Date: Thu, 27 Nov 2008 09:11:17 +0100 Mime-Version: 1.0 Sent to CCL by: =?ISO-8859-1?Q?=D6d=F6n?= Farkas [farkas]_[chem.elte.hu] Hi David, It is not really possible to say what to do in general in a case like yours. Many kind of problems may occur, like the bonding of the stacked molecules. To try to solve this choose two proper atoms (A1 and A2) in the two molecules and add A1 A2 B to get proper bonding between the stacked molecules. You might freeze the bond angles defined for this bond then. If zou have more choices to connect stacked molecules you might add all of them. Of course, this will just help the description of the motions of atoms with redundant internals and should not affect the result. If you have further questions contact me directly. Best wishes, Ödön On Mon, 2008-11-24 at 08:28 -0500, David Close closed[*]etsu.edu wrote: > Sent to CCL by: "David Close" [closed(~)etsu.edu] > I'm having a problem imposing constraints on a series of stacked molecules. I'm trying to look at the influence of neighbors in a problem involving a crystal structure. When I get up to three molecules in a stack the middle molecule tends to move away from the stack. I need to impose constraints, but I keep getting a message "Curvilinear step not converged. Error in constraints". Thuis is in GAussian. On another system the program seems to fuss about symmetry? > My questions is, what calculations are being performed to decided whether or not a constraint is suitable? If one knows what calculations were being perfomred, is it possible to add suitable constraints? It seems as if a few bond constraints work, but when I add constrained angles, the curvilinear message appears after 100 "tries".> > -- Ödön Farkas Associate professor Deparment of Organic Chemistry and Laboratory of Chemical Informatics, Institute of Chemistry, Eötvös Loránd University, Budapest Address: 1/A Pázmány Péter sétány, H-1117 Budapest, Hungary Phone: +36-1-372-2570 Cell phone: +36-30-255-3111 Fax: +36-1-372-2620 URL: http://organ.elte.hu/farkas