From owner-chemistry #at# ccl.net Fri Nov 4 11:14:00 2005 From: "Marc Baaden baaden.__.smplinux.de" To: CCL Subject: CCL: Dipole moment calculation from non-zero charge distribution Message-Id: <-29879-051104105915-9637-N0KpUWeSoBXMULGKXj98qg__server.ccl.net> X-Original-From: Marc Baaden Content-Type: text/plain; charset=us-ascii Date: Fri, 04 Nov 2005 16:13:14 +0100 Mime-Version: 1.0 Sent to CCL by: Marc Baaden [baaden%a%smplinux.de] David, thank you for the very enlightening comments, suggestions and references. >>> "David F. Green dfgreen:+:ams.sunysb.edu" said: >> The standard definition of the dipole moment holds regardless of the net >> charge. [..] Hmm, I'd like to ask: what is the standard definition of a molecular dipole ? In several textbooks I found definitions along the line of "A dipole is a pair of electric charges of equal magnitude but opposite polarity [..]" which *implies* that the net charge is zero. This was also IMHO the "classical" and somewhat intuitive definition. I guess the second moment definition as integral over charge times position vector would be a better/more general definition. But what makes these definitions equivalent or allows to expand from one to the other ? (The first definition a priori breaking down for charged species) Also there must be a rationale to discard other definitions, eg one could dream up a definition of a molecular dipole as sum of all bond dipoles ? Are there seminal references on this ? Thanks, Marc Baaden -- Dr. Marc Baaden - Institut de Biologie Physico-Chimique, Paris mailto:baaden_-_smplinux.de - http://www.baaden.ibpc.fr FAX: +33 15841 5026 - Tel: +33 15841 5176 ou +33 609 843217