CCL: interpretation the Natural Bond Orbitals (NBO) results

Dear May,

NBO constructs a localized set of orbitals (based on atom-centered hybrid AOs) which fall into the categories (at least for closed-shell systems): BD (bonding, 2 electrons significantly shared between two atoms), BD* (antibonding, same as above, but the hybrids are out of phase/antibonding), LP (2 electrons only significantly present on one atom), LP* (same as above but formally empty, can have significant population from delocalization from BD or LP orbitals), and finally RY* which come from your polarization/diffuse functions and shouldn't be significantly populated.

You didn't list the other atom in each bond you showed in your post, but it looks like you have one orbital that is technically Ru-Ru bonding but is only 4% on the other Ru3, and a technically antibonding orbital that is mostly on Ru3. The population of one is ca. 0.66 electrons and the other is ca. 0.48 electrons so the net Ru-Ru interaction is basically non-bonding, e.g. there are two non-interacting lone pairs, one on each Ru. They are listed as bonds because the sharing is greater than the cutoff for considering them lone pairs (just barely).

You can buy GENNBO5.0 and run an archive file (generated in NBO3) through it, which allows you to do a canonical molecular orbital analysis. Some program packages suck as ADF and Jaguar come with this utility program. This shows you the contributions of each NBO to the MOs, and breaks down each interaction by % bonding/nonbonding/antibonding. To do this, run NBO3.0 with "pop=nboread" in the Route section and "$nbo archive file=yourfilename $end" after your molecular spec, custom basis sets, etc. This will generate "yourfilename.47", which you open and edit so the second line reads "$NBO cmo $END. Then run GENNBO on it and you will get a repeat of the NBO output, but with the CMO section included.

As for if NBO is appropriate for metal-metal bonding, that depends on if the model chemistry you are using is appropriate for metal-metal bonding, because the NBO analysis is just "reshuffling" the orbitals calculated in your ESS program. Very often those interactions are quite multiconfigurational in character, so HF would fail and DFT would be questionable. Additionally, the NBO formalism is a little vague in some instances with regard to DFT (the 2nd order pert. analysis is suspect for instance) so treat results with a critical eye.

Hope this helps somewhat.

Regards,
Jamin



On Sat, Mar 6, 2010 at 2:08 AM, may abdelghani may01dz##yahoo.fr <owner-chemistry*o*ccl.net> wrote:

Dear CCL'ers

1. What we mean by the world "antibond BD*" in the output of NBO; or I have in my NBO output the flowing sentences:

575. (0.66522) BD ( 1)Ru 3-Ru 4     

                (  4.23%)   0.2056*Ru 3 s( 76.43%)p 0.04(  2.89%)d 0.27( 20.69%)

576. (0.47855) BD*( 1)Ru 3-Ru 4     

                ( 95.77%)   0.9786*Ru 3 s( 76.43%)p 0.04(  2.89%)d 0.27( 20.69%)

The question is: I have a bond between the atom Ru3 and Ru4 or not…what is the bonding character of this bond?


2. There is any relationship between the «cluster valence electron" concept and the results of «Natural Electron Configuration"?


4. In terms of single, double and triple bonds, where  we classify that of  non-Lewis-type NBOs  : BD*, RY* and LP?


5. Can the version 3 of NBO software, NBO.3, give a credibility description of metal-metal bond?

thank a lot for all,




--
Jamin L Krinsky, Ph.D.
Molecular Graphics and Computation Facility
175 Tan Hall, University of California, Berkeley, CA 94720
jamink*o*berkeley.edu, 510-643-0616
http://glab.cchem.berkeley.edu">http://glab.cchem.berkeley.edu