From owner-chemistry@ccl.net Tue May  7 12:41:01 2013
From: "Reis Heribert hreis_-_eie.gr" <owner-chemistry{=}server.ccl.net>
To: CCL
Subject: CCL:G: Dipole moment of charged species in Gaussian
Message-Id: <-48652-130507122614-15680-Vxvhh/a4HAixAMBuAr3i4w{=}server.ccl.net>
X-Original-From: Reis Heribert <hreis-*-eie.gr>
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Date: Tue, 7 May 2013 18:26:08 +0200
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Sent to CCL by: Reis Heribert [hreis---eie.gr]
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Hello

The definition of the dipole moment of a charged species is well defined.
The only problem with it (and with all higher multipoles) is, that its
value depends on the origin of the coordinate system. Thus for comparison
purposes the origin of the coordinate system of different molecules should
be comparable. A very common choice is the centre of mass; another
possibility is the center of nuclear charge, which is the standard origin
in Gaussian09, if one does not specify the 'Nosymm' keyword. You can also
turn the problem on its head and define the origin as that point where the
dipole is zero...

I'm assuming that you want to compare the absolute value of the dipole
between different molecules. In case you also want to compare the
components, you also should use comparable orientations of the coordinate
systems (e.g the coordinate system where e.g. the inertia (or
polarizability or ...) tensor is diagonal). This, however, is independent
of being charged or uncharged.

Heribert

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<div dir=3D"ltr"><div><div><div>Hello<br><br></div>The definition of the di=
pole moment of a charged species is well defined. The only problem with it =
(and with all higher multipoles) is, that its value depends on the origin o=
f the coordinate system. Thus for comparison purposes the origin of the coo=
rdinate system of different molecules should be comparable. A very common c=
hoice is the centre of mass; another possibility is the center of nuclear c=
harge, which is the standard origin in Gaussian09, if one does not specify =
the &#39;Nosymm&#39; keyword. You can also turn the problem on its head and=
 define the origin as that point where the dipole is zero...<br>

<br></div>I&#39;m assuming that you want to compare the absolute value of t=
he dipole between different molecules. In case you also want to compare the=
 components, you also should use comparable orientations of the coordinate =
systems (e.g the coordinate system where e.g. the inertia (or polarizabilit=
y or ...) tensor is diagonal). This, however, is independent of being charg=
ed or uncharged.<br>

<br></div>Heribert<br></div>

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