From owner-chemistry@ccl.net Fri Jul 22 05:12:39 2005 From: "CCL" To: CCL Subject: CCL: dissociation problem in PCM model ? Message-Id: <-28917-050722051146-13078-eSc6C2yCCSce8pLLLmWjCA###server.ccl.net> X-Original-From: Elmar Gerwalin Content-Disposition: inline Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 Sent to CCL by: Elmar Gerwalin Hi ! First, thanks to all who answerded to my question (see below). Now, some days, emails and outputs later, I know the reason for the error I observed: The don't arise from the fact that 2 cavities are built. Due to Prof. Cammi (main PCM contributor to Gaussian), PCM is able to handle systems with multiple cavities well (Tomasi, J. Comp.Chem. 8 , 778 (1987)) The dissociation problem I observed does not apppear in Turbomole or g03, if one uses the default RADII. These methods show correct asymptotic behaviour (E -> E(K+)+E(A-)) But (!), in g98 a different model (UAHF) is used by default to assign the radii. In this model, different radii are use to treat isolated ions and bound atoms (e.g. Cl, CH3O). Different radii result in different solvation energies... g03 does not show this "artifact" as the model UA0 used therein uses the same radii for the same atoms/groups in all cases. To get correct (smooth) potential energy curves by g98, one has to specify the radii of the anions by using a PCM option like NSFE (see gaussian manual). Bye, Elmar The original question to CCL: > X> I'm trying to describe dissociation processes in some small > X> organic molecules. > X> Therefore, I'm using B3LYP+SCRF(C-PCM, solvent=methanol) single > X> point jobs to get the > X> solvation energy at each step. Finally, a potential energy curve > X> E(R) is my goal. > X> R is the bond distance I'm interested in; e.g. a C-O, C-Cl bond > X> or , for testing purposes > X> Na-Cl. > X> > X> But, unfortunately, wrong asymptotic behaviour (like a "size > X> inconsistency problem") is > X> observed in all cases: the "supermolecule's" solvation energy at > X> large distances (10 or 20 A) > X> is differing about more than 20 kcal/mole from the sum of the > X> solvation energies of the two ions. > X> > X> My question is: is the problem known (references ?)? How can be > X> it be accounted for ? > X> Do I have to use specific energy terms given in gaussian's > X> output and/or male a correction to them ? > X> > X> Any help is appreciated. > X> > X> Bye, > X> > X> Yours, > X> Elmar > X> > X> > X> -- > X> ======================================================== > X> Elmar Gerwalin , University of Kaiserslautern,Germany > X> Dept. of Theoretical Chemistry > X> elg###chemie.uni-kl.de > X> ======================================================== > X> From owner-chemistry@ccl.net Fri Jul 22 05:51:37 2005 From: "CCL" To: CCL Subject: CCL: about basis set contraction Message-Id: <-28918-050721125030-22035-eSc6C2yCCSce8pLLLmWjCA(-)server.ccl.net> X-Original-From: Pierre Archirel Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=ISO-8859-1; format=flowed MIME-Version: 1.0 Sent to CCL by: Pierre Archirel Dear collegues, A fully uncontracted basis set can always be (partly) contracted with the simple rule: 1- perform an scf calculation of the atom in the uncontracted basis 2- the s primitive gaussians with the largest exponents can be contracted together with the coefficients they take in the expansion of the 1s, as long as these coefficients are proportionnal. More precisely: If c(i,j) is the coefficient of primitive j in orbital i, contract together the 1,2 ... n primitives, if c(2,1)/c(1,1)=c(3,1)/c(2,1)= ... up to c(2,n)/c(1,n)=c(3,n)/c(2,n)=... 3- the rule is the same for the p, d ... orbitals Best wishes __________________________________________________________ Pierre Archirel Groupe de Chimie Théorique Laboratoire de Chimie Physique Tel: 01 69 15 63 86 Bat 349 Fax: 01 69 15 61 88 91405 Orsay Cedex France pierre.archirel(-)lcp.u-psud.fr __________________________________________________________ From owner-chemistry@ccl.net Fri Jul 22 10:14:02 2005 From: "CCL" To: CCL Subject: CCL: RSC Modern molecular modelling - realise the benefits Message-Id: <-28919-050722100118-29582-eSc6C2yCCSce8pLLLmWjCA=-=server.ccl.net> X-Original-From: "INDUSTRY (shared)" Content-class: urn:content-classes:message Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Sent to CCL by: "INDUSTRY (shared)" Find out what modern molecular modelling could do for you and your organisation! 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