From chemistry-request@www.ccl.net Fri Jan 15 04:49:47 1999 Received: from host11.lctn.u-nancy.fr (host11.lctn.u-nancy.fr [192.54.210.15]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id EAA06785 Fri, 15 Jan 1999 04:49:46 -0500 (EST) From: aplincou@host11.lctn.u-nancy.fr Received: (from aplincou@localhost) by host11.lctn.u-nancy.fr (AIX4.2/UCB 8.7/8.7) id KAA28332 for chemistry@www.ccl.net; Fri, 15 Jan 1999 10:48:02 +0100 (NFT) Date: Fri, 15 Jan 1999 10:48:02 +0100 (NFT) Message-Id: <199901150948.KAA28332@host11.lctn.u-nancy.fr> To: chemistry@www.ccl.net Subject: Spin contamination Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-MD5: fXgyzyLaobDuuax51oMEjQ== Dear CCL'ers I am studying the OO bond cleavage in the secondary ozonide (in order to form a biradical .OCH2OCH2O. ) at the MP2 and DFT level (singlet state). The barrier heights computed with Gaussian94 are : UMP2/6-31G** = 43.4 kcal/mol Annihilation of the first spin contaminant: S**2 before annihilation .8871, after .0785 PMP2/6-31G** = 20.9 kcal/mol UB3LYP/6-31G** = 20.8 kcal/mol Annihilation of the first spin contaminant: S**2 before annihilation .7684, after .0234 I would know your opinion about the reliability of this PMP correction in which the largest spin contaminant is annihilated. What about the spin contamination in the UB3LYP method (PMP2 and UB3LYP are very close...) ? References are welcome. I will summarize. Thanks a lot. Phil ------------------------------------------------------------------------ APLINCOURT Philippe Laboratoire de Chimie Theorique UMR 7565 Structure et Reactivite des Systemes Moleculaires Complexes Faculte des Sciences, Domaine Scientifique Victor Grignard B.P. 239 54506 VANDOEUVRE-LES-NANCY Cedex Tel : 03 83 91 20 00 Poste 35 52 Fax : 03 83 91 25 30 E-mail : Philippe.Aplincourt@lctn.u-nancy.fr ------------------------------------------------------------------------ From chemistry-request@www.ccl.net Thu Jan 14 03:09:48 1999 Received: from zzmkgtw.zzmk.unizh.ch (zzmkgtw.unizh.ch [130.60.67.3]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with SMTP id DAA23669 Thu, 14 Jan 1999 03:09:47 -0500 (EST) Received: by zzmkgtw.zzmk.unizh.ch; (5.65v3.2/1.3/10May95) id AA15666; Thu, 14 Jan 1999 09:09:46 +0100 Message-Id: <3.0.3.32.19990114091453.0068988c@highdent> X-Sender: toukie@highdent (Unverified) X-Mailer: QUALCOMM Windows Eudora Light Version 3.0.3 (32) Date: Thu, 14 Jan 1999 09:14:53 +0100 To: chemistry@www.ccl.net From: "Hr. Dr. S. Shapiro" Subject: MOPAC question Cc: toukie@zui.unizh.ch Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Dear Colleagues; I have a couple of questions about the internal workings of the MOPAC optimisation algorithms: Consider a large molecule A-B, where A and B are separate portions of the molecule connected to one another by a single sigma bond (C-C, C-O, or C-N). The units A and B have been optimsed in terms of bond lengths, angles, and dihedral angles, but the A-B bond is not optimal (and in fact may be rather far from optimal). Now suppose you do a MOPAC run with all optimisation flags set on "1" and the keywords "am1 ef precise". (a) Will MOPAC recognise that the two moieties A and B are already optimised and so more-or-less leave their "internal structures" alone whilst focussing its attention on optimising the A-B link, or will it "deoptimise" and then "reoptimise" the whole structure? (b) Suppose that instead of all optimisation flags being set to "1" those for moiety A are set to "0" whilst those for moiety B and for the A-B link are set to "1". Will MOPAC "drag" the intact optimised moiety B over to A in the course of optimising the A-B link, or will it "deoptimise" and then "reoptimise" the whole B moiety? Thanks in advance to all responders, S. Shapiro toukie@zui.unizh.ch