From owner-chemistry@ccl.net Sat Jan 14 18:43:00 2006 From: "Robinson, James James.Robinson-.-evotec.com" To: CCL Subject: CCL: Semiempirical examples for teaching: success stories Message-Id: <-30501-060114183818-1026-3bMyOfKH7ok6n7Bjyh5K8g*server.ccl.net> X-Original-From: "Robinson, James" Content-class: urn:content-classes:message Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="us-ascii" Date: Sat, 14 Jan 2006 22:53:33 -0000 MIME-Version: 1.0 Sent to CCL by: "Robinson, James" [James.Robinson\a/evotec.com] Not everyone has time and resources to run resource hungry calculations, for instance QCISD(T) or even B3lYP/6-311+(2d,p), sometimes a calculation to simply disprove/support an idea is adequate. The biggest stumbling block is the failure of us all to come up with something quicker than SCF algorithms for ab initio calculations. There are instances when semi-empirical calculations take minutes and provide an adequate qualitative answer. I think Feynmann said if theories don't match experiment scrap the theory..okay which ab initio, DFT, semi-empirical calc satisfies that. Work with the tools you have and some chemistry knowledge. Think; do not accept blindly and do not stick to your own ideas because of vanity. None of the calculations are perfect or ever big enough to mimic reality. Dr J J Robinson, UK. -----Original Message----- > From: owner-chemistry a ccl.net [mailto:owner-chemistry a ccl.net] Sent: 14 January 2006 03:47 To: Robinson, James Subject: CCL: Semiempirical examples for teaching: success stories Sent to CCL by: Terry Frankcombe [T.Frankcombe[]chem.leidenuniv.nl] *cough* *splutter* Sorry James, but that's complete nonsense (to put it politely). Since when have semiempirical extrapolations* been taken over experimental data? Complete codswallop. A lot of the claims you make in that paper are questionable at best. What you have shown are best interpreted as FAILURES of semiempirical and DFT methods, not wins. Terry *I say extrapolations to highlight that semiempirical methods applied outside their training set are not much more than guesses. Informed guesses, but guesses nonetheless. -- Dr Terry Frankcombe LIC / Theoretical Chemistry University of Leiden Postbus 9502, 2300 RA Leiden, The Netherlands Ph. +31 71 527 4533 Fax +31 71 527 4397 > Sent to CCL by: "James J. P. Stewart" [mrmopac||worldnet.att.net] > --=====================_177286794==.ALT > Content-Type: text/plain; charset="us-ascii"; format=flowed > > My apologies: My last message re semiempirical methods contained > invalid URLs