From chemistry-request@www.ccl.net Mon Nov 23 10:41:38 1998 Received: from hartree.chem.kuleuven.ac.be (hartree.quantchem.kuleuven.ac.be [134.58.49.1]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id KAA06597 Mon, 23 Nov 1998 10:41:31 -0500 (EST) Received: from localhost (steven@localhost) by hartree.chem.kuleuven.ac.be (8.9.0/8.9.0) with ESMTP id QAA51712 for ; Mon, 23 Nov 1998 16:41:06 +0100 Date: Mon, 23 Nov 1998 16:41:06 +0100 (NFT) From: Steven Creve To: Computational Chemistry List Subject: CCL:DFT:KS exact? Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Hi, in Kohn-Sham theory, the density is written as a sum over orbitals squared. The occupation numbers of these orbitals are 1 or 0. My question: can the density of _any_ molecular system be written in this way? Or, in other words, are there systems where one needs fractional occupation numbers to represent the exact density? If the answer to the latter question is 'yes' then one might question if KS-DFT yields _in principle_ (if the exact Exc is known) the exact density. _any_ comments are most welcome, Steven -------------------------------------------------------------------------- Steven Creve steven.creve@chem.kuleuven.ac.be Labo Quantumchemie Celestijnenlaan 200F 3001-HEVERLEE tel: (32) (16) 32 73 93 BELGIUM fax: (32) (16) 32 79 92 From chemistry-request@www.ccl.net Mon Nov 23 13:07:06 1998 Received: from mx02.uni-tuebingen.de (root@mx02.uni-tuebingen.de [134.2.3.12]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id NAA13973 Mon, 23 Nov 1998 13:07:04 -0500 (EST) Received: from theseus (theseus.pharm.chemie.uni-tuebingen.de [134.2.68.91]) by mx02.uni-tuebingen.de (8.8.8/8.8.8) with SMTP id TAA08259 for ; Mon, 23 Nov 1998 19:06:49 +0100 Date: Mon, 23 Nov 1998 19:06:49 +0100 Message-Id: <199811231806.TAA08259@mx02.uni-tuebingen.de> X-Sender: cpcmu01@cpcmu01.mail.uni-tuebingen.de X-Mailer: Windows Eudora Light Version 1.5.2 Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" To: chemistry@www.ccl.net From: Inge Muszynski Subject: Mopac_Keyword Dear CCL'lers, is it obligatory to use the keyword charge when minimizing charged molecules within Mopac? Many thanks in advance. Inge Muszynski From chemistry-request@www.ccl.net Mon Nov 23 14:35:25 1998 Received: from sctmg02.sct.ucarb.com ([140.170.101.20]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id OAA22553 Mon, 23 Nov 1998 14:35:24 -0500 (EST) Received: by sctmg02.sct.ucarb.com with Internet Mail Service (5.0.1458.49) id ; Mon, 23 Nov 1998 14:35:41 -0500 Message-ID: From: "Smith JA (Jack)" To: "'Steven Creve'" Cc: "'CCL'" Subject: RE: DFT:KS exact? Date: Mon, 23 Nov 1998 14:28:22 -0500 X-Priority: 3 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.0.1458.49) Content-Type: text/plain > in Kohn-Sham theory, the density is written as a sum over orbitals > squared. The occupation numbers of these orbitals are 1 or 0. My > question: > can the density of _any_ molecular system be written in this way? Or, > in > other words, are there systems where one needs fractional occupation > numbers to represent the exact density? If the answer to the latter > question is 'yes' then one might question if KS-DFT yields _in > principle_ > (if the exact Exc is known) the exact density. > > _any_ comments are most welcome, > There is a direct connection (equivalence) between DFT/KS with exact exchange and Grand Canonical HF, where the density operator is formally expressed in terms of fractional occupation numbers representing a Grand Canonical ensemble. See the following: (1) Jorgensen and Ohrn, Phys Rev A, 8(1), p112 (1973). (2) Abdulnur, Linderberg, Ohrn and Thulstrup, Phys Rev A, 6(3), p889 (1972). and compare with Slater's Hyper-HF (3) Slater, Mann, Wilson and Wood, Phys Rev, 184(3), p672 (1969). - Jack -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Jack A. Smith || Union Carbide || Phone: (304) 747-5797 Catalyst Skill Center || FAX: (304) 747-4672 P.O. Box 8361 || S. Charleston, WV 25303 || smithja@ucarb.com -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-