# CCL: Dipole moment calculation from non-zero charge distribution

*From*: Marc Baaden <baaden\a/smplinux.de>
*Subject*: CCL: Dipole moment calculation from non-zero charge
distribution
*Date*: Fri, 04 Nov 2005 16:13:14 +0100

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