From kwonohy@mail.auburn.edu Thu May 7 02:29:23 1998 Received: from mallard.duc.auburn.edu for kwonohy@mail.auburn.edu by www.ccl.net (8.8.3/950822.1) id CAA27738; Thu, 7 May 1998 02:09:00 -0400 (EDT) Received: from preinstalledcom by mallard.duc.auburn.edu (SMI-8.6/SMI-SVR4) id BAA06052; Thu, 7 May 1998 01:08:57 -0500 Message-ID: <35514ECE.6168@mail.auburn.edu> Date: Thu, 07 May 1998 01:03:58 -0500 From: Ohyun Kwon Reply-To: kwonohy@mail.auburn.edu Organization: Auburn University X-Mailer: Mozilla 3.04 (Win95; I) MIME-Version: 1.0 To: chemistry@www.ccl.net Subject: pi stacking interactions Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Dear CCL's; Is anybody who has some experiences or knoledges on the theoretical calculations of pi stacking interactions? I am now calculating this interactions for conjugated polymer system using AM1 method but the results seems to be a little bit doubtable. I would greatly appreciate it if anybody give me some advices on this matter. I am looking forward to haring from you soon. Ohyun Kwon Department of Chemistry Auburn University Auburn, AL 36849 email) kwonohy@mail.auburn.edu From salvat@host21.lctn.u-nancy.fr Thu May 7 06:29:31 1998 Received: from host21.lctn.u-nancy.fr for salvat@host21.lctn.u-nancy.fr by www.ccl.net (8.8.3/950822.1) id GAA28401; Thu, 7 May 1998 06:15:11 -0400 (EDT) From: Received: (from salvat@localhost) by host21.lctn.u-nancy.fr (AIX4.2/UCB 8.7/8.7) id MAA15498 for chemistry@www.ccl.net; Thu, 7 May 1998 12:07:34 +0200 (DFT) Date: Thu, 7 May 1998 12:07:34 +0200 (DFT) Message-Id: <199805071007.MAA15498@host21.lctn.u-nancy.fr> To: chemistry@www.ccl.net Subject: Re: pi-stacking interactions Dear CCLers, Many theoretical studies on pi-stacking interactions have been achieved. Ab initio calculations yield satisfactory results if high level theoretical levels are used. See: P. Hobza, H. L. Selzle, E. W. Schlag, Chem. Rev. 1994, 94, 1767 and references therein. C. Chipot, R. Jaffe, B. Maigret, D. A. Pearlman, P. A. Kollman, J. Am. Chem. Soc. 1996, 118, 11217. An AM1 study on arene-arene complexes has been published: V. E. Williams, R. P. Lemieux, G. R. J. Thatcher, J. Org. Chem. 1996, 61, 1927. According to the authors, the results "showed good agreement with literature data on related experimental systems". In my opinion, the agreement is purely qualitative. I think that semiempirical methods are not adequate for pi-stacking studies due to their poor performance of medium-range interactions: V. Buss, J. Messinger, N. Heuser, QCPE Bull. 1991, 11, 5. G. I. Csonka, J. Comp. Chem. 1993, 14, 895. G. I. Csonka, J. G. Angyan, J. Mol. Struct. (THEOCHEM) 1997, 393, 31. Finally, MM3 method has been specifically parametrised in order to consider pi interactions: N. L. Allinger, Z.-q. Zhu, K. Chen, J. Am. Chem. Soc. 1992, 114, 6120. However, I think that there are not specific studies on the performance of the MM3 method on pi-stacking interactions. Luis Salvatella Departement de Chimie Theorique Universite de Nancy I France From chipot@host7.lctn.u-nancy.fr Thu May 7 04:24 EDT 1998 Received: from host7.lctn.u-nancy.fr for chipot@host7.lctn.u-nancy.fr by www.ccl.net (8.8.3/950822.1) id EAA28068; Thu, 7 May 1998 04:24:45 -0400 (EDT) Received: (from chipot@localhost) by host7.lctn.u-nancy.fr (AIX4.2/UCB 8.7/8.7) id KAA30034 for chemistry-request@www.ccl.net; Thu, 7 May 1998 10:07:43 +0200 (DFT) From: Message-Id: <199805070807.KAA30034@host7.lctn.u-nancy.fr> Subject: Re: CCL:pi stacking interactions To: chemistry@www.ccl.net (Ohyun Kwon) Date: Thu, 7 May 1998 10:07:43 +0200 (DFT) In-Reply-To: <35514ECE.6168@mail.auburn.edu> from "Ohyun Kwon" at May 7, 98 01:03:58 am X-Mailer: ELM [version 2.4 PL23] Content-Type: text There have been a number of theoretical investigations on pi-stacking, at various levels of approximation. You can look at the work of Hobza, Selzle and Schlag, J. Chem. Phys. 1990, 93, 5893; J. Phys. Chem. 1993, 97, 3937; J. Am. Chem. Soc. 1994, 116, 3500; Chem. Rev. 1994, 94, 1767. Those essentially cover ab initio studies of the benzene dimer. Worth looking at is the paper of Karlstrom et al., J. Am. Chem. Soc. 1983, 105, 3777. More recently, the work of Jaffe and Smith, J. Chem. Phys. 1996, 105, 2780, and J. Phys. Chem., 100, 9624 presents benchmark QM calculations for that system. On the statistical simulation side, the work of Linse, J. Am. Chem. Soc 1990, 114, 1744; 1992, 114, 4366; 1993, 115, 8793 is an important one. Equally interesting is the paper of Jorgensen and Severance, J. Am. Chem. Soc. 1990, 112, 4768, on the orientational averaged potential of mean force of the benzene dimer. Very recently, we reinvestigated this problem at the QM and MM levels of approximation. Chipot et al., J. Am. Chem. Soc. 1996, 118, 11217. Best wishes, Chris _______________________________________________________________________ Chris Chipot, Ph.D. Laboratoire de Chimie Theorique Phone: (33) 3-83-91-25-96 U.M.R. C.N.R.S. No 7565 Fax: (33) 3-83-91-25-30 Universite Henri Poincare - Nancy I B.P. 239 54506 Vandoeuvre-les-Nancy Cedex E-mail: chipot@lctn.u-nancy.fr `The light shines through the darkness and the darkness has not overcome it' _______________________________________________________________________ From s.m.todd@chem.hull.ac.uk Wed May 6 07:29:13 1998 Received: from mailhub4.hull.ac.uk for s.m.todd@chem.hull.ac.uk by www.ccl.net (8.8.3/950822.1) id GAA22784; Wed, 6 May 1998 06:37:46 -0400 (EDT) Received: from humus.ucc.hull.ac.uk by lehar.ucc.hull.ac.uk; Wed, 6 May 1998 11:30:45 +0100 Received: from attilla.hull.ac.uk [150.237.108.105] by humus.ucc.hull.ac.uk with esmtp (Exim 1.60 #1) id 0yX1TJ-0001Dc-00; Wed, 6 May 1998 11:30:45 +0100 Message-ID: <35503BEE.DCDDCD87@chem.hull.ac.uk> Date: Wed, 06 May 1998 11:31:10 +0100 From: Stevie T X-Mailer: Mozilla 4.01 [en] (Win95; I) MIME-Version: 1.0 To: ccl Subject: semi-empirical calculations.... X-Priority: 3 (Normal) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Hi all... I have recently been doing some dipole moment calculations using the AM1 and PM3 semi-empirical methods in Hyperchem. I have been trying the caculations at different torsion angles and obtaining some reasonable results. However, occasionally a difference as small as 10 degrees makes the dipole moment value increase from 4D to about 4000D. Has anyone else had this problem ? What do people think of the accuracy of semi-empirical calculations for such properties as dipole moments ? Also, when the calculations were repeated under Mopac/AM1 and Mopac/PM3 in Cerius2 they yielded reasonable results. I presume this is to do with the individual ways in which the two similar methods are implemented under different packages (ie Hyperchem and Mopac). Has anyone any ideas on this or any references to work done on this ? Cheers in advance... and I'll summarise... Steve Todd -- "I used to think the brain was the most important organ in the body, 'til I realized yeah, look what's telling me that." -- Emo Phillips mail to : S.M.Todd@chem.hull.ac.uk web-site: http://www.hull.ac.uk/php/chpsmt/