From jsl@virgil.ruc.dk Tue Oct 14 06:30:32 1997 Received: from emma.ruc.dk for jsl@virgil.ruc.dk by www.ccl.net (8.8.3/950822.1) id GAA08020; Tue, 14 Oct 1997 06:29:20 -0400 (EDT) Received: from virgil.ruc.dk (virgil.ruc.dk [130.225.220.110]) by emma.ruc.dk (8.8.5/8.8.5) with ESMTP id MAA14839; Tue, 14 Oct 1997 12:30:27 +0200 (MET DST) Received: from VIRGIL/MAILQUEUE by virgil.ruc.dk (Mercury 1.21); 14 Oct 97 12:20:27 +0100 Received: from MAILQUEUE by VIRGIL (Mercury 1.21); 14 Oct 97 12:20:18 +0100 From: "Jens Spanget-Larsen" Organization: Roskilde Universitetscenter To: "Eugene G. Noda" Date: Tue, 14 Oct 1997 12:20:15 +0100 Subject: Re: CCL:Absorption spectra from ZINDO/S CC: chemistry@www.ccl.net Priority: normal X-mailer: Pegasus Mail for Windows (v2.23) Message-ID: <1C1E6730FB3@virgil.ruc.dk> Eugene G. Noda : > In Options Dialog Box (Setup Menu) for ZINDO/S method there > are the Overlap Weighting Factors, which can be manually modified > in the region 0-2. Default values of sigma-sigma parameter is > 1,267 and pi-pi parameter is 0,64. > > So the questions is: > > 1. Whether we can change these parameters to calculate the correct > absorption spectra and how the values of these parameters ought to > be estimated? Dear Eugene: The choice of the pi-pi overlap weighting factor in ZINDO/S is crucial to the results of the model. Unfortunately, HyperChem has chosen to adopt the value 0.64 as the default value. This is very misleading, because in almost all practical applications, one should adopt a value close to 0.585. Krassimir Stavrev thus recently communicated the following details regarding the choice of overlap weighting factor: Stavrev, Krassimir , Mon, 21 Jul 1997: | ..... The value of 0.64 has been successfully used for | triplets spectroscopy, in which case it was shown to yield better | results than the 0.585 factor, see the original work of Zerner and | co-authors quoted in the Computational Chemistry manual, p.295. The | other value, 0.585, is most commonly used in the studies of | transition-metal and organic systems. To my knowledge, the 0.64 value | has not been very well tested and was applied only to triplet-triplet | excitations. In view of this situation, it is not understandable why HyperChem has chosen to adopt 0.64 as the default value, a choice that is likely to lead many users astray! Yours, Jens >--< =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= JENS SPANGET-LARSEN Phone: +45 4674 2000 (RUC) Department of Chemistry +45 4674 2710 (direct) Roskilde University (RUC) Fax: +45 4674 3011 P.O.Box 260 E-Mail: JSL@virgil.ruc.dk DK-4000 Roskilde, Denmark http://www.ruc.dk/dis/chem/psos/ =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=