From chemistry-request ":at:" server.ccl.net Mon May 13 16:56:46 2002 Received: from mail-b.bcc.ac.uk ([144.82.100.22]) by server.ccl.net (8.11.6/8.11.0) with ESMTP id g4DKujJ08925 for ; Mon, 13 May 2002 16:56:45 -0400 Received: from socrates-a.ucl.ac.uk by mail-b.bcc.ac.uk with SMTP (Mailer) with ESMTP; Mon, 13 May 2002 21:56:44 +0100 Received: (from uccatvm: at :localhost) by socrates-a.ucl.ac.uk (8.11.6+Sun/8.9.3) id g4DKuhe03012; Mon, 13 May 2002 21:56:43 +0100 (BST) From: uccatvm Message-Id: <200205132056.g4DKuhe03012-!at!-socrates-a.ucl.ac.uk> Subject: counterpoise with LMP2 To: chemistry {*at*} ccl.net (CCL) Date: Mon, 13 May 2002 21:56:43 +0100 (BST) Cc: T.vanMourik(+ at +)ucl.ac.uk (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, I am wondering what the most correct way is to do counterpoise with local MP2. In the local MP2 method originally proposed by Pulay (Chem.Phys.Lett. 100, 151, 1983), to each localised MO a subset (orbital domain) of the virtual orbitals is assigned. To calculate the interaction energy of a weakly interacting system, the orbital domains of the subsystems are first determined at large distance, and used in subsequent dimer calculations at smaller intermolecular distances (as recommended in for example Schutz et al., J. Phys. Chem. 102, 5997, 1998). Now, I assume that (to keep a true counterpoise) it is best to use the orbital domains determined at large distance for the monomer+ghost calculation. For this, one would first have to determine the domains of the monomer+ghost with the ghost at large R, and use the thus obtained orbital domains in the monomer+ghost calculation at the smaller distance. What do people think? Would this be the correct way of doing it? Of course, the BSSE is strongly reduced in LMP2, and should in principle be negligible when using an appropriate basis set. However, when using small basis sets it may not be negligible, and I would like to know the best way of doing counterpoise for these cases. Thanks in advance, 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[ AT ]netcomuk.co.uk http://www.chem.ucl.ac.uk/people/vanmourik/index.html =====================================================================