CCL: NBO vs Loewdin Charges



I think what is meant is that if you represent the electron density correctly, the net atomic charges should be independent of the basis set used.
Methods that do not satisfy this property (such as Mulliken populations) are non-physical and should be discarded.
It is possible to construct atomic population analysis methods in which the atomic populations depend only on the electron and spin density distributions with no explicit basis set dependence.
In this latter case, even an experimentally measured electron distribution could be used as input without requiring a "basis set" at all.

Sincerely,

Tom





On Mon, Aug 31, 2015 at 11:06 PM, Dr. Robert Molt Jr. r.molt.chemical.physics+/-gmail.com <owner-chemistry],[ccl.net> wrote:
Atomic charge models are not basis independent; see Chris Cramer's book, chapter 9, p.314. Some models give charges which are consistent with increasing basis set size, some are not, but all depend on the basis.

If you have anions, you cannot describe the density correctly without diffuse functions; this is a basis set dependence.
Dr. Robert Molt Jr.
 r.molt.chemical.physics]-[gmail.com
On 08/31/2015 11:14 PM, John McKelvey jmmckel(a)gmail.com wrote:
Hello,

There is a paper from a group in Germany demonstrating essentially basis set independence of atomic charges....  Terrible to say that while I remember the paper, and that the method has been installed in ORCA for the next release, I will have to search for the paper...  just moved from Indiana to Missouri so things are in a bit of disarray.

Maybe someone has seen this paper?


John
 

On Mon, Aug 31, 2015 at 5:47 PM, Víctor Luaña Cabal victor_-_fluor.quimica.uniovi.es <owner-chemistry/a\ccl.net> wrote:

Sent to CCL by: =?iso-8859-1?Q?V=EDctor_Lua=F1a?= Cabal [victor ~~ fluor.quimica.uniovi.es]
On Mon, Aug 31, 2015 at 04:22:51PM -0400, Jim Kress jimkress35-x-gmail.com wrote:
>
> Sent to CCL by: "Jim Kress" [jimkress35]-[http://gmail.com" rel="noreferrer" target="_blank">gmail.com]
> Did you use an ECP for Plutonium and if so, was it properly represented in
> the AIM analysis?

Jim,

QTAIM should refer to the all electron density. However there have
been explorations of using ECP valence densities and they can work if
you do it carefully. You can either add the core contributions to the
valence density (it works) or be advise that your electron density is
not complete, so there are properties of the real QTAIM analysis that
can not work.

For instance, the basins and the topological partition of the full
electron density (rho) is not equivalent if you are using only the
valence component (val-rho).

However, if the basins are well defined there is no problem in
integrating the valence density within the full electron rho. The same
can be said for the analysis of spin components, and so on.
Using the critic2 code a lot of strange numerical experiments of
this kind can be easily performed. The code also has techniques to
fulfill the valence density with core components.

Read on critic2 in this ref.

A. Otero-de-la-Roza et al, Comput phys Commun 182 (2013) 2232--2248

An updated version of the code and manual can be found on

<http://azufre.quimica.uniovi.es/software.html#critic2>
<http://schooner.chem.dal.ca/wiki/Critic2>

I may look for old work published on this subject, if you are truly
interested.

Best regards,
             Víctor Luaña
--
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