From owner-chemistry@ccl.net Fri Mar 12 06:27:00 2021 From: "Reza Shojaei shojaei81===gmail.com" To: CCL Subject: CCL:G: Dipole moment calculations in Gaussian Message-Id: <-54290-210312062431-25706-kA/hNupAVNKEuhDcTbrv2w**server.ccl.net> X-Original-From: "Reza Shojaei" Date: Fri, 12 Mar 2021 06:24:28 -0500 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. Can we find a correlation between dipole moment and Mulliken charges or they are totally irrelevant topics? Regards, Reza From owner-chemistry@ccl.net Fri Mar 12 09:27:00 2021 From: "Mariusz Radon mariusz.radon^^gmail.com" To: CCL Subject: CCL:G: Dipole moment calculations in Gaussian Message-Id: <-54291-210312092625-14702-eoJWfQ1igQWhhmqYRQgSyQ-.-server.ccl.net> X-Original-From: Mariusz Radon Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=utf-8 Date: Fri, 12 Mar 2021 15:26:15 +0100 Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.4\)) Sent to CCL by: Mariusz Radon [mariusz.radon**gmail.com] > On 12 Mar 2021, at 12:24, Reza Shojaei shojaei81===gmail.com 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