From owner-chemistry@ccl.net Tue Nov 4 17:04:00 2008 From: "Kalju Kahn kalju=-=chem.ucsb.edu" To: CCL Subject: CCL: maximum displacement Message-Id: <-38025-081104162847-32246-qjY9DWTj4Oo28uXrBihlZg-.-server.ccl.net> X-Original-From: "Kalju Kahn" Content-Transfer-Encoding: 8bit Content-Type: text/plain;charset=iso-8859-1 Date: Tue, 4 Nov 2008 13:28:28 -0800 (PST) MIME-Version: 1.0 Sent to CCL by: "Kalju Kahn" [kalju+/-chem.ucsb.edu] Orlin, If you loosen these criteria too much, you will have a successful calculation but the structure found will be too far from the true minimum. Being able to do a calculation is not the same thing as being able to get the correct result. If you really want to neglect displacement conditions, just use the geometry that gave the results below (or pick a geometry with the lowest energy from your search). Your forces are small, the PES must be very flat in the region you are in: large changes in the structure will cause only small change in energy. You may want to make sure that your structure is a minimum, not a saddle point or a some plateau via frequency calculation. You should not have negative frequencies. After the frequency calculation, it will not hurt to try Opt=ReadFC, Geom=Check; you might find a better structure quickly using the correct Hessian. Kalju > > Sent to CCL by: Orlin Blajiev [blajiev%x%vub.ac.be] > Hi, > > I will appreciate an advise how to relax Maximum Displacement condition > (or neglect it althogether). I am already using IOP(1/7=1200). > > Maximum Force 0.000275 0.001800 YES > RMS Force 0.000063 0.001200 YES > Maximum Displacement 0.125614 0.007200 NO > RMS Displacement 0.017703 0.004800 NO > > Thank in advance. > > Orlin > > Orlin Blajiev > Electrochemical and Surface Engineering (SURF) > Faculty of Applied Science > Vrije Universiteit Brussel > Pleinlaan 2 - 1050 Brussels - Belgium > tel: ++32 2 6293538 - fax: ++32 2 6293200> > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dr. Kalju Kahn Department of Chemistry and Biochemistry UC Santa Barbara, CA 93106