From chemistry-request ^%at%^ server.ccl.net Wed Jul 19 08:35:14 2000 Received: from terra.ifi.unicamp.br (terra.ifi.unicamp.br [143.106.6.20]) by server.ccl.net (8.8.7/8.8.7) with ESMTP id IAA31339 for ; Wed, 19 Jul 2000 08:34:51 -0400 Received: from ifi.unicamp.br (lua [143.106.6.13]) by terra.ifi.unicamp.br (8.9.3/8.9.3) with ESMTP id JAA10321 for ; Wed, 19 Jul 2000 09:32:17 -0300 (BSC) Received: (from daemon -8 at 8- localhost) by ifi.unicamp.br (8.9.3/8.9.3) id JAA11101 for ; Wed, 19 Jul 2000 09:32:14 -0300 (BSC) Received: from giselle.ifi.unicamp.br(143.106.72.217) via SMTP by lua.ifi.unicamp.br, id smtpdAAAa002hR; Wed Jul 19 09:32:12 2000 Message-Id: <4.3.2.7.0.20000719091727.00b3a2d0 $#at#$ lua.ifi.unicamp.br> X-Sender: dasf -x- at -x- lua.ifi.unicamp.br X-Mailer: QUALCOMM Windows Eudora Version 4.3.2 Date: Wed, 19 Jul 2000 09:21:55 -0300 To: CHEMISTRY {*at*} ccl.net From: Demetrio Antonio da Silva Filho Subject: CI-Singles Summary Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1"; format=flowed Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by server.ccl.net id IAA31348 Original post: Dear Netters, I'm in doubt about the CI-Singles method and the number of single substitutions that this method uses on its calculation. In Pople's paper (J. B. Foresman, M. Head-Gordon, J. A. Pople and M. J. Frisch, Toward a Systematic Molecular Orbital Theory for Excited States, J. Phys. Chem. 96, 135 (1992).) the CI-Singles method is defined as configuration interaction among "all" singly substituted determinants. In Gaussian manual, there is a keyword for this method (NStates) which sets the number of states that will be solved. This keyword (Mstates) sets the number of states used in the CI expansion of the wavefunction or independent of the number used in this keyword all singly substituted determinants will be used? Thanks in advance, Demetrio FIlho Replies! =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-==-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Dear Demetrio! The Gaussian keyword CIS implies a CI-Singles calculation with inclusion of "all" singly excited configurations (however, core levels are usually not included in the CI). The NStates option specifies how many excited states should be calculated; the default value is 3. The value of NStates has no effect on the number of configurations included in the CI. Yours, Jens >--< =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-==-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Dear Antonio, This keyword (Mstates) sets the number of states to solve for and this does not affect the number of determinants (precisely: CSF) in the CI expansion (which is Nocc x Nvirt of course). Stefan _________________________________________________________ Prof. Dr. Stefan Grimme Organisch-Chemisches Institut (Abt. Theoretische Chemie) Westfaelische Wilhelms-Universitaet, Corrensstrasse 40 D-48149 Muenster, Tel (+49)-251-83 36512/33241/36515(Fax) Email:grimmes %-% at %-% uni-muenster.de http://www.uni-muenster.de/Chemie/OC/research/grimme/ _________________________________________________________ =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-==-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Hello, I think that Gaussian does not diagonalize the complete CIS matrix to get the eigenvectors (and eigenvalues), but rather solve the problem iteratively for each eigenvector. Then the CIS matrix contains all singly excited determiants, but Gaussian gives you only the first "Nstates" eigenvectors. I don't know if I am right, but that the way I understand it. Hope this helps. ...Xav Ast. Pr. Xavier Assfeld Xavier.Assfeld ^at^ lctn.u-nancy.fr Laboratoire de Chimie theorique (T) 33 3 83 91 21 49 Universite Henri Poincare (F) 33 3 83 91 25 30 F-54506 Nancy BP 239 http://www.lctn.u-nancy.fr =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-==-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Dear Demetrio, The Nstates keyword in gaussian determines the number of excited states whose energies and other properties are solved for using CIS. It doesn't affect the number of single excitations used in the CI. Best regards, Sam Abrash Dear Demetrio, The CIS method is indeed configuration interaction among all singly substituted determinants. That is, the electronic Hamiltonian is represented in a basis consisting of only determinants which are single orbital-substitutions away from a reference (usually the Hartree-Fock determinant). Once you have this CIS Hamiltonian, you can extract its eigenvalues, which represent energies of electronically excited states. The keyword "NStates" denotes the number of eigenvalues of the CIS Hamiltonian you wish to obtain, not the number of singly excited determinants used for the representation of H. -Daniel -- T. Daniel Crawford Department of Chemistry crawdad ^%at%^ vt.edu Virginia Polytechnic Institute and www.chem.vt.edu/chem-dept/crawford State University =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-==-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- _____________________________________ Demetrio A. da Silva Filho UNICAMP - IFGW Prédio D - Sala 17 CEP 13083-970 C.Postal 6165 Campinas - SP - Brasil _____________________________________ "Se não houver frutos, valeu a beleza das flores. Se não houver flores, valeu a sombra das folhas. Se não houver folhas, valeu a intenção da semente." Henfil