From chemistry-request@server.ccl.net Sat Sep 7 18:06:39 2002 Received: from ivory.trentu.ca ([192.75.12.103]) by server.ccl.net (8.11.6/8.11.0) with ESMTP id g87M6c318147 for ; Sat, 7 Sep 2002 18:06:38 -0400 Received: from trentu.ca ([206.248.117.30]) by trentu.ca (PMDF V5.2-32 #37862) with ESMTP id <01KM88FMP3DC000TYU@trentu.ca> for chemistry@ccl.net; Sat, 7 Sep 2002 18:06:34 EDT Date: Sat, 07 Sep 2002 18:08:48 -0400 From: elewars Subject: SUMMARY size-consistent AND variational To: chemistry@ccl.net Message-id: <3D7A78F0.36DBFCB6@trentu.ca> MIME-version: 1.0 X-Mailer: Mozilla 4.79 [en] (WinNT; U) Content-type: text/plain; charset=iso-8859-1 Content-transfer-encoding: 8BIT X-Accept-Language: en 2002 Sept 7 SUMMARY of answers; I am sory if I have omitted anyone. I thank all who responded. EL Question 2002 Aug 25 Hello, Does anyone know of a method (correlation level, like HF, MP, CI, CASSCF, etc.) besides HF and full CI that is both size consistent AND variational? Thanks. E. Lewars --------------------- Answers #1(a) This ref. might be of interest: A.I. Krylov, "Spin-flip configuration interaction: an electronic structure model that is both variational and size-consistent", Chem.Phys.Lett. 350 (2001) 522-530 Have a nice day, Mikael J. http://www.chem.helsinki.fi/~mpjohans/ 1(b) [...what do you think about CASSCF and size consistency?...] I don't know that much about CASSCF, but I would think it is size-consistent, at least if the active space is chosen properly. But don't take my word for it :-) Have a nice day, Mikael J. http://www.helsinki.fi/~mpjohans/ ----------------- #2 Dear Dr. Lewars, Variational in the sense of being an extremum of some functional are the coupled-pair-functional (CPF) and the averaged coupled pair functional (ACPF) from the Ahlrichs group. These methods are also nearly size consistent. However, the energies they give are not an upper bound to the lowest eigenvalue of the Hamiltonian (they are bounded from below though). Recently Anna Krylov has published some papers on "spin flip CI" in JCP and CPL. This method is, for a restricted set of problems, both, size-consistent and variational. It has other shortcomings but I enjoyed the general idea because its is simple and appealing. Apart from that nothing pops up at first glance; please let me know if you get interesting responses! Hope that helps, best regards, Frank ___________________________________________________________________________ PD Dr. Frank Neese Tel. +49-208-306-3657 Max Planck Institut für Strahlenchemie E-mail: neese@mpi-muelheim.mpg.de Stiftstr. 34-36 Mülheim an der Ruhr Germany http://www.mpi-muelheim.mpg.de/strneu/index_e.htm ___________________________________________________________________________ #3 Spin-unrestricted geminal theory based on strongly orthogonal geminals. Its general (not necessary size consistent) form is known as SEP or APSG, see P. Surjan in Topics in Current Chemistry, vol. 203, pp 63-88 for review. The rigorously size consistent form is SSG, see V. Rassolov, JCP, in print (Oct. 2002). I can send you a preprint if you're really interested. Vitaly Rassolov Dept. of Chemistry and Biochemistry (803) 777-7811 University of South Carolina fax (803) 777-9521 631 Sumter St Columbia, SC 29208 rassolov@mail.chem.sc.edu -------------------------------------------------------------- #4 ACPF or AQCC may be close to what you are looking for. Galina ------------------------------------ Dr. Galina Chaban NASA Ames Research Center Mail Stop T27B-1 Moffett Field, CA 94035-1000 Tel (650) 604-4995 Fax (650) 604-1095 e-mail: chaban@nas.nasa.gov --------------------------------------------------- #5 "Van Dam, HJJ (Huub)" CASSCF should be provided that you choose your active orbitals correctly. DFT should be size consistent as well. That's it... Huub van Dam --------------------------------------------------------- =================================== ======================