CCL:G: Dipole moment calculations in Gaussian

 Sent to CCL by: Mariusz Radon [mariusz.radon**]
 > On 12 Mar 2021, at 12:24, Reza Shojaei
 <owner-chemistry/a\> wrote:
 > Sent to CCL by: "Reza  Shojaei" [shojaei81*]
 > 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 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\ (mariusz.radon/a\