From laidig@pg.com Sat Sep 16 14:31:49 1995 Received: from oldspice.pg.com for laidig@pg.com by www.ccl.net (8.6.10/950822.1) id OAA29791; Sat, 16 Sep 1995 14:19:53 -0400 Received: by oldspice.pg.com (8.6.11/8.6.9) id OAA03012 for <@oldspice.pg.com:CHEMISTRY@www.ccl.net>; Sat, 16 Sep 1995 14:13:56 -0400 Received: from morpheus by pandora via ESMTP (950511.SGI.8.6.12.PATCH526/930416.SGI.AUTO) for <@pandora.na.pg.com:CHEMISTRY@www.ccl.net> id OAA04864; Sat, 16 Sep 1995 14:18:21 -0400 Received: by morpheus (950413.SGI.8.6.12/930416.SGI.AUTO) id OAA01068; Sat, 16 Sep 1995 14:18:21 -0400 Date: Sat, 16 Sep 1995 14:18:21 -0400 From: laidig@pg.com (Bill Laidig) Message-Id: <9509161418.ZM1066@morpheus.na.pg.com> In-Reply-To: laidig@pg.com (Bill Laidig) "CCL:Information about MEDLA" (Sep 7, 10:11am) References: <9509071338.AA01245@rchsg8.chemie.uni-regensburg.de> <9509071011.ZM3403@morpheus.na.pg.com> X-Mailer: Z-Mail (3.2.1 6apr95 MediaMail) To: CHEMISTRY@www.ccl.net Subject: Summary - Information about MEDLA Cc: laidig@morpheus.na.pg.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii A week or so ago I sent the following post: >All, > >In a recent C&E News article an approximate electronic structure method >called MEDLA by Prof. P.G. Mezey was discussed. I was asked by my boss if >this really was the greatest invention since sliced bread as the article >implied. Since I am not familar with this method I was wondering if any >of you have thoughts on the subject. Also, is this technique similar >to Yang's divide-and-conquer approach? I will summarize to the list if >I get any responses. Bill I only received one response here it is: ******************************************************************************* Hi ; I don't know much about MEDLA but my understanding is that MEDLA is QUITE DIFFERENT from the divide-and-conquer method. MEDLA is a procedure to "flesh out" a nuclei configuration with an approximate electron density without doing a first-principles calculations: instead, it assembles in "some way" fragment densities that were previously calculated and saved in a library. Apparently this density is accurate enough to get reliable Molecular Electrosatic Potential, and this (MEP) is a key physical quantity for molecules of biological interests. But I would GUESS that the total energy probably cannot be obtained to any useful degree of accuracy using only the MEDLA density as input because: (1) the best "density-only" kinetic energy functionals are still not very good, which is one reason why people still do SCF Kohn-Sham calculations; (2) small differences between trial and converged SCF density can give significant errors on total energy differences. Still, using a MEDLA input density (which should be at least "fairly accurate") together with a one-iteration-only Harris functional calculation might be a way to get accurate total energies (nearly as accurate as a full blown SCF calculation?) at relatively low computational cost (say, roughly 20 times less than a conventional SCF calculation requiring 20 iterations). If that's the case, MEDLA could be the greatest invention since ... the muffin tin potential. Rene Fournier. |-------------------------------|-----------------------------| | Rene Fournier | fournier@physics.unlv.edu | | Department of Physics | fournie@ned1.sims.nrc.ca | | University of Nevada | phone : (702) 895 1706 | | Las Vegas, NV 89154-4002 USA | FAX : (702) 895 0804 | |-------------------------------|-----------------------------| -- ****************************************************************************** * "Like jewels in a crown, the precious stones glittered in the queen's * * round metal hat." - Jack Handey * * * * Bill Laidig * * The Procter & Gamble Co. tel 513-627-2857 fax - 1233 * * Miami Valley Laboratories laidig@pg.com (preferred) * * P.O. Box 538707 wd_laidig@pg.com * * Cincinnati, OH 45253-8707 laidig@qtp.ufl.edu * ******************************************************************************