|
hello, It sounds strange to me that some people are using different basis sets for optimization and frequency calculations. In principle, the geometry is no longer at the minimum of the PES when the BS is changed, and in the case of frequency jobs, one can get imaginary frequencies. Pascal Close, David M. CLOSED^mail.etsu.edu wrote: Sent to CCL by: "Close, David M." [CLOSED__mail.etsu.edu] Yes, that is exactly right. As a check you could try a frequency calc. using the same basis set. Usually 3 out of 4 of the "yes" are ok. For some reason the third "yes" is sometimes a "no". I don't know why. Now a more basic question. If you are taking a course on doing calculations, you are always told you must use the same basis sets in frequency calculations as on the original optimizations. But people seem to be getting away from this are very large calculations. If it takes a week to do an optimization, it might take 3-4 weeks to do a frequency calculation. So people are now using smaller basis sets to do faster frequency calcs. I do not happen to know if this leads to problems. I do know that Berny Schlegel warned about this some time ago, but I do not know the current thinking on this. -----Original Message-----From: owner-chemistry ~~ ccl.net [mailto:owner-chemistry ~~ ccl.net]Sent: Monday, August 25, 2008 11:29 AM To: Close, David M. Subject: CCL:G: End of a frequency job Sent to CCL by: Orlin Blajiev [Orlin.Blajiev,vub.ac.be] David, Alcides, Thanks for the info. I guess G03 reports the geometry as non-converged because I use different BS in Opt and Freq. Best regards, Orlin Alcides Simao alsimao[#]gmail.com wrote: -- Dr. Pascal Boulet, Computational Chemist University of Provence Laboratoire Chimie Provence, UMR6264 Centre Saint-Jerome, case MADIREL F-13397 MARSEILLE Cedex 20, France Tel. +33 (0) 491 63 71 17 Fax. +33 (0) 491 63 71 11 courriel: pascal.boulet|,|univ-provence.fr http://www.lc-provence.fr http://allos.up.univ-mrs.fr/boulet |