From chemistry-request: at :server.ccl.net Tue Jul 9 15:14:10 2002 Received: from ucidoor.unitedcatalysts.com ([208.23.162.2]) by server.ccl.net (8.11.6/8.11.0) with ESMTP id g69JEAp01678 for ; Tue, 9 Jul 2002 15:14:10 -0400 Received: by ucidoor.unitedcatalysts.com; (8.8.8/1.3/10May95) id PAA20828; Tue, 9 Jul 2002 15:14:09 -0400 (EDT) Received: from 10.1.0.50 by ucismtp02.unitedcatalysts.com (InterScan E-Mail VirusWall NT); Tue, 09 Jul 2002 15:11:57 -0400 Received: from lvlxch01.unitedcatalysts.com ([10.16.100.88]) by lvlmail.unitedcatalysts.com (PMDF V6.0-24 #41777) with ESMTP id <0GYZ00EERX5D0Q %-% at %-% lvlmail.unitedcatalysts.com>; Tue, 09 Jul 2002 15:08:01 -0400 (EDT) Received: by lvlxch01.unitedcatalysts.com with Internet Mail Service (5.5.2653.19) id <31QX4X55>; Tue, 09 Jul 2002 15:11:24 -0400 Content-return: allowed Date: Tue, 09 Jul 2002 15:11:18 -0400 From: "Shobe, Dave" Subject: RE: CHELPG To: "'George Hall'" , "'CCL'" Message-id: <157A51F55AAAD3119CD70008C7B1629D01C15E4F |-at-| lvlxch01.unitedcatalysts.com> MIME-version: 1.0 X-Mailer: Internet Mail Service (5.5.2653.19) Content-type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by server.ccl.net id g69JEAp01679 Mulliken charges are assigned to atoms based on the "usage" of the atoms' basis functions in the molecular orbitals that are calculated. It is known as a quick-and-dirty way of assigning charges, but one that doesn't necessarily have any physical meaning. Mulliken charges are notoriously basis-set dependent. CHELPG charges are based on the electrostatic field generated by the molecule. It is a best-fit method; the set of charges produced by the CHELPG method are the point charges that would produce an electric field which is as similar as possible to the molecule's. Accordingly, if you need the charges for molecular-mechanics calculations which include electrostatic interactions, CHELPG is arguably the best for that purpose. There are other methods of assigning atomic charges. GAPT charges are based on the derivative of the molecular dipole moment WRT the atomic positions. AIM charges are based on the division of 3-dimensional space among the atoms in the molecule, according to a surface that has certain mathematical properties. NBO charges are similar to Mulliken charges, but the orbitals are transformed into "natural" orbitals, which fixes some of the basis-set dependency of the Mulliken method. --David Shobe Süd-Chemie Inc. phone (502) 634-7409 fax (502) 634-7724 email dshobe {*at*} sud-chemieinc.com Don't bother flaming me: I'm behind a firewall. -----Original Message----- From: George Hall [mailto:georgehalli%!at!%hotmail.com] Sent: Tuesday, July 09, 2002 10:21 AM To: chemistry-: at :-ccl.net Subject: CCL:CHELPG Hi everybody, I wonder if some could point me out what are the differences between Chelpg charges and Mulliken. Would you please indicate me some references or some advices about the aproach for these kind of charges. Thanks a lot in advance. George Hall. _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com -= This is automatically added to each message by mailing script =- CHEMISTRY-: at :-ccl.net -- To Everybody | CHEMISTRY-REQUEST-: at :-ccl.net -- To Admins Ftp: ftp.ccl.net | WWW: http://www.ccl.net/chemistry/ | Jan: jkl ":at:" ccl.net