# CCL:G: Dipole moment calculations in Gaussian

*From*: Mariusz Radon <mariusz.radon() gmail.com>
*Subject*: CCL:G: Dipole moment calculations in Gaussian
*Date*: Fri, 12 Mar 2021 15:26:15 +0100

Sent to CCL by: Mariusz Radon [mariusz.radon**gmail.com]
> On 12 Mar 2021, at 12:24, Reza Shojaei shojaei81===gmail.com
<owner-chemistry/a\ccl.net> wrote:
>
>
> Sent to CCL by: "Reza Shojaei" [shojaei81*gmail.com]
> Dear ccl users,
>
> I use Gaussian09 to calculate the rotation effect of a functional group on
> the dipole moment and some other physical properties of Paracetamol. so
> far, I found no clear description of how Gaussian computes the dipole
> moment. Would you please send a reference about the mechanism that Gaussian
> uses to calculate the dipole moment.
Dear Reza:
Well, this should be pretty straightforward, based on one-particle density
matrix (to describe electronic distribution after completing the SCF) and matrix
elements of x,y,z operators (one electron integrals), and of course also point
charges on all nuclei (+Z_i).
I hope that you obviously recall the fact that dipole moment is not uniquely
defined for a charged molecule? In such cases the definition is of course
arbitrary and may be even different in different programs (but most probably it
is defined with respect to the mass center in most of them).
>
> Can we find a correlation between dipole moment and Mulliken charges or
> they are totally irrelevant topics?
Different topics. You should not expect the Mulliken charges on atoms to explain
the electrostatic properties, like dipole moment. Take a look at ECP charges,
maybe they could give a better explanation because they are meant to reproduce
the electrostatic potential at least somewhere. Or "Cummulative Atomic
Multipole Representation of the Molecular Cherge Distributuion”
(10.1016/0009-2614(83)80208-5) if you really need to “decompose”
the dipole moment into atomic contributions.
Best wishes,
Mariusz
--
Mariusz Radon, Ph.D., D.Sc.
Assistant Professor
Faculty of Chemistry, Jagiellonian University
Address: Gronostajowa 2, 30-387 Krakow, Poland
Room C1-06, Phone: 48-12-686-24-89
E-mail: mradon/a\chemia.uj.edu.pl (mariusz.radon/a\uj.edu.pl)
Web: http://www2.chemia.uj.edu.pl/~mradon
ORCID: https://orcid.org/0000-0002-1901-8521