From chemistry-request {*at*} ccl.net Thu Jan 8 05:41:53 2004 Received: from smtp2.ruc.dk (smtp2.ruc.dk [130.225.220.22]) by server.ccl.net (8.12.8/8.12.8) with ESMTP id i08AfLX9018083 for ; Thu, 8 Jan 2004 05:41:22 -0500 Received: by smtp2.ruc.dk (Postfix, from userid 1001) id 57D6F2384EA; Thu, 8 Jan 2004 11:41:20 +0100 (CET) Received: from virgil.ruc.dk (virgil.ruc.dk [130.225.220.110]) by smtp2.ruc.dk (Postfix) with ESMTP id 3CE6823848E; Thu, 8 Jan 2004 11:41:14 +0100 (CET) Received: from VIRGIL/SpoolDir by virgil.ruc.dk (Mercury 1.47); 8 Jan 04 11:41:17 +0100 Received: from SpoolDir by VIRGIL (Mercury 1.47); 8 Jan 04 11:41:14 +0100 From: "Jens Spanget-Larsen" Organization: Roskilde Universitetscenter To: "John McKelvey" Date: Thu, 8 Jan 2004 11:40:50 +0100 Subject: Re: CCL:Summary: Calculations without Born-Oppenheimer approximation "2nd Call" Reply-To: spanget*at*ruc.dk Cc: boehm*at*pc07.pc.chemie.tu-darmstadt.de, chemistry*at*ccl.net Message-ID: <3FFD41C2.13095.4C9827 _-at-_)localhost> Priority: normal In-reply-to: <001d01c3d3b7$f2b044e0$6501a8c0 # - at - # goofy> X-mailer: Pegasus Mail for Windows (v4.01) X-Spam-Checker-Version: SpamAssassin 2.55 (1.174.2.19-2003-05-19-exp) X-Spam-Report: X-Spam-Status: No, hits=-1.0 required=7.0 tests=IN_REP_TO,QUOTED_EMAIL_TEXT version=2.55 X-Spam-Level: "John McKelvey" : > Jens, > > A question, please. Neglecting the fact that FSGO's may be poor basis > functions, where do they stand with respect to BO if the positions of the > gaussians are optimized along with the SCF process? > > Regards, > > John McKelvey > Dear John: I don't have the papers at hand. But as far as I see, the basic features of the approach by Boehm and associates are the following: They perform the basic calculations within the usual Born-Oppenheimer approximation, obtaining data for a very large number of nuclear configurations. This part of the investigation can be performed with a variety of electronic hamiltonians and basis sets, as in other standard ab initio procedures. However, and that is the important point, they don't determine the molecular "equilibrium configuration" in the usual Born-Oppenheimer manner, i.e., by selecting the single nuclear configuration that corresponds to a minimum on the Born-Oppenheimer potential hypersurface. In the Boehm procedure, the quantum and thermal nuclear degrees of freedom are accounted for by forming quantum ensemble averages over the set of nuclear configurations. The result is a wave-packet picture of the nuclear positions that goes beyond the Born- Oppenheimer picture. Yours, Jens >--< =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= JENS SPANGET-LARSEN Office: +45 4674 2710 Department of Chemistry Fax: +45 4674 3011 Roskilde University (RUC) Mobile: +45 2320 6246 P.O.Box 260 E-Mail: spanget*at*ruc.dk DK-4000 Roskilde, Denmark http://virgil.ruc.dk/~spanget =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=