From owner-chemistry;at;ccl.net Mon Nov 24 08:36:01 2008 From: "David Close closed[*]etsu.edu" To: CCL Subject: CCL:G: Constraints? Message-Id: <-38159-081124082851-6758-fcIp3GgMp+OCm9qOfA95ZA-#-server.ccl.net> X-Original-From: "David Close" Date: Mon, 24 Nov 2008 08:28:47 -0500 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".