From Schiffer@MSMWIA.hoechst.hoechst-ag.d400.de Thu Oct 24 06:31:49 1996 Received: from ixgate02.dfnrelay.d400.de for Schiffer@MSMWIA.hoechst.hoechst-ag.d400.de by www.ccl.net (8.8.0/950822.1) id GAA22432; Thu, 24 Oct 1996 06:16:23 -0400 (EDT) X400-Received: by mta d400relay in /PRMD=dfnrelay/ADMD=d400/C=de/; Relayed; Thu, 24 Oct 1996 11:19:50 +0200 X400-Received: by /PRMD=HOECHST-AG/ADMD=D400/C=DE/; Relayed; Thu, 24 Oct 1996 11:16:59 +0200 X400-Received: by /PRMD=HOECHST-AG-MSM2/ADMD=DBP/C=DE/; Relayed; Thu, 24 Oct 1996 11:14:58 +0200 X400-Received: by /PRMD=HOECHST-AG-MSM/ADMD=DBP/C=DE/; Relayed; Thu, 24 Oct 1996 15:14:52 +0200 Date: Thu, 24 Oct 1996 15:14:52 +0200 X400-Originator: Schiffer@MSMWIA.hoechst.hoechst-ag.d400.de X400-Recipients: non-disclosure:; X400-MTS-Identifier: [/PRMD=HOECHST-AG/ADMD=D400/C=DE/;0009700003738719000002] X400-Content-Type: P2-1984 (2) Content-Identifier: CSI NC V3.0 From: "Schiffer, Heinz, Dr., WIA / SC" Message-ID: <004DAC30.MAI*/S=Schiffer/OU=MSMWIA/O=HOECHST/PRMD=hoechst-ag/ADMD=dbp/C=de/@MHS> To: CCL (Receipt Notification Requested) (Non Receipt Notification Requested) Subject: Charges Hi all, from time to time there is a discussion about the construction and the use of point charges in molecules. I think there is no doubt within the community, that for intermolecular interactions one should use charges ( and point dipoles, point quadrupoles, etc ) which are adjusted to reproduce as good as possible the electrostatic potential of the molecule. For qualitative discussions of chemical bonding the use of various population analysis ( Mulliken; Davidson-Roby-Ahlrichs, natural orbital populations of Weinhold; Bader; etc. By the way : There is a very promising new one of Marco Haeser in JACS, Vol. 118, 1996, pp. 7311-7325, which I think is more rigorous as any previous ones and without any ad hoc postulates.) are most appropriate. The fitting of the electrostatic potential of a molecule is a highly non-trivial subject ( see e.g. Michelle Miller Francl et al., J. Comput. Chem., Vol. 17, 1996, pp. 367-383, and the very recent review by Sarah L. Price, J. Chem. Soc., Faraday Trans., Vol. 92, 1996, pp. 2997-3008 ) and in my view not a really solved problem, especially for large molecules. Now I became aware of a series of papers by George G. Hall and his coworkers about the fitting of electron densities, which I never heart off bevor and which, I think, are quite unknown to the community. Hall et al. fit the calculated electron densities of molecules to atom-centered gaussians as it is done by many DFT-programs ( "density fitting with an auxillary basis" ) and got a very good ( in my view an excellent ) representation of the electrostatic potential of a molecule. Those DFT- programs with charge density fitting are able to calculate the charge density of molecules within density functional theory with more than thousand basis functions on a single workstation in about an hour of cpu-time ( see e.g. Karin Eichkorn et al., Chem. Phys. Lett. 240 (1995) 283-290 ). As a by-product of the calculation one gets an excellent fit of the electrostatic potential of the molecule with gaussians. After some minor modifications of the programs one gets from this point charges, point dipoles, point quadrupoles, etc. or if one likes it the current bun model of Hall and coworkes. My question to the community is now, wether anyone else has similar thoughts or even experiences with this sort of density fitted electrostatic potentials ? Does anyone has an opinion about using such charge models in force field calculations ( energy minimization of molecular crystals or molecular dynamics calculation of fluids ) ? Please send responses to the list, so that anyone else can follow the discussion. Ciao, Heinz PS: Here are the references of Hall and coworkers : George G. Hall and David Martin Approximate Electron Densities for Atoms and Molecules Isr. J. Chem. 19 (1980) 255-259 G. G. Hall and C. M. Smith Fitting Eelectron Densities of Molecules Int. J. Quantum Chem. 25 (1984) 881-890 G. G. Hall and K. Tsujinaga The molecular electrostatic potential of some simple molecules Theor. Chim. Acta 69 (1986) 425-436 K. Tsujinaga and G. G. Hall The currant bun model of simple molecules Theor. Chim. Acta 70 (1986) 257-264 ---------------------------------------------------------------------------- ----------------------------------------------- Dr. Heinz Schiffer 65926 Frankfurt am Main Hoechst AG Phone ++49-69-305-2330 Scientific Computing Fax ++49-69-305-81162 Email : schiffer@wia.hoechst-ag.d400.de schiffer@msmwia.hoechst.hoechst-ag.d400.de ---------------------------------------------------------------------------- -----------------------------------------------