From chemistry-request@ccl.net Sun Dec 1 09:35:49 1991 Date: Sun, 1 Dec 1991 08:19 CDT From: Andy Holder Subject: PM3 Charges To: CHEMISTRY@ccl.net Charges with PM3 are traditionally suspect and has been noted before. The problems with charge inversion (as you describe with nitrogen) are especially severe. The basis of this problem is a chemically poor set of parameters that are corrected by some rather extreme Gaussian functions. The reliability of AM1 as compared with much more advanced methods in charge prediction has been illustrated rep- eatedly. If charges (and other electronic properties for that matter) interest you, I would recommend sticking with AM1. =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= DR. ANDREW HOLDER Department of Chemistry || BITNET Addr: AHOLDER@UMKCVAX1 University of Missouri - Kansas City || Internet Addr: aholder@vax1.umkc.edu Spencer Chemistry, Room 502 || Phone Number: (816) 235-2293 Kansas City, Missouri 64110 || FAX Number: (816) 235-1717 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=