From chemistry-request {*at*} ccl.net Thu Jul 3 06:58:25 2003 Received: from mail-b.bcc.ac.uk (mail-b.bcc.ac.uk [144.82.100.22]) by server.ccl.net (8.12.8/8.12.8) with ESMTP id h63AwPqe027720 for ; Thu, 3 Jul 2003 06:58:25 -0400 Received: from socrates-a.ucl.ac.uk by mail-b.bcc.ac.uk with SMTP (Mailer) with ESMTP; Thu, 3 Jul 2003 11:58:24 +0100 Received: (from uccatvm[ AT ]localhost) by socrates-a.ucl.ac.uk (8.11.7+Sun/8.9.3) id h63AwND19813; Thu, 3 Jul 2003 11:58:23 +0100 (BST) Message-Id: <200307031058.h63AwND19813.-at-.socrates-a.ucl.ac.uk> Subject: CCL:re DFT and small basis sets To: chemistry.-at-.ccl.net (CCL) Date: Thu, 3 Jul 2003 11:58:23 +0100 (BST) Cc: T.vanMourik.-at-.ucl.ac.uk (Tanja van Mourik) In-Reply-To: <3F02ECDD.D642E01A.-at-.trentu.ca> from "elewars" at Jul 02, 2003 10:31:57 AM From: Tanja van Mourik X-Mailer: ELM [version 2.5 PL3] MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Hi All, Lynch, Zhao and Truhlar advocate including diffuse functions on non-hydrogenic atoms when calculating reaction energies, barrier heights and conformational energies with DFT, see: J Phys Chem A 107 (9): 1384-1388 (2003). So I would recommend using 6-31+G* rather than 6-31G* as the smallest basis set for yielding accurate results. Tanja -- ===================================================================== Tanja van Mourik Royal Society University Research Fellow Chemistry Department University College London phone: +44 (0)20-7679-4663 20 Gordon Street e-mail: work: T.vanMourik.-at-.ucl.ac.uk London WC1H 0AJ, UK home: tanja_van_mourik.-at-.btopenworld.com http://www.chem.ucl.ac.uk/people/vanmourik/index.html ===================================================================== > > Re "Has anyone ever published a discussion of the accuracy of DFT at > small basis sets?" > > I'm not sure just what you consider small (most workers now would likely > say that > 6-31G* is small), but DFT calculations are known to be saturated by > basis > functions more quickly than are ab initio calculations. Here are three > refs: > > 1) "Once the double split-valence level is reached, further improvement > in basis > set quality offers little in the way of structutal or energetic > improvement." G. > N. Merrill, S. Gronert, and S. R. Kass. J Phys Chem, 1997, _101_, 204. > > 2) "Our results also show that B3LYP calculations converge rapidly with > > increasing basis set size and that the cost-to-benefit- ratio is optimal > at the > 6-31G* basis set level. 6-31G* will be the basis set of choice in B3LYP > calculations on much larger molecules [than C4H6O2]." P. J. Stephens, F. > J. > Devlin, C. F. Chablowski, and M. J. Frisch, J Phys Chem, 1994, _98_, > 11623, and > refs therein. > > 3) In defiance of tradition, the unequivocally small 3-21G(*) set has > been used > to optimize carbene geometries: H. M. Muchall, N. H. Werstiuk, and B. > Chodhurry, > Can J Chem, 1998, _76_, 221. > > (You my also find some useful info in E. Lewars, "Computational > Chemistry", > Kluwer, 2003; section 7.3.2.2). > > E. Lewars > ======== > > Ed Brothers wrote: > > > Folks: > > Has anyone ever published a discussion of the accuracy of DFT at > > small basis sets? > > > > Ed. > > Merz group. > > Penn State. > > > > > > -= This is automatically added to each message by mailing script =- > To send e-mail to subscribers of CCL put the string CCL: on your Subject: line > and send your message to: CHEMISTRY.-at-.ccl.net > > Send your subscription/unsubscription requests to: CHEMISTRY-REQUEST.-at-.ccl.net > HOME Page: http://www.ccl.net | Jobs Page: http://www.ccl.net/jobs > > If your mail is bouncing from CCL.NET domain send it to the maintainer: > Jan Labanowski, jkl.-at-.ccl.net (read about it on CCL Home Page) > -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > > > > > >