# CCL:G: CMO Analysis of a roB3LYP calculation using Gaussian 09 and NBO
6

*From*: "Johannes Straub"
<johannes.straub::aci.uni-heidelberg.de>
*Subject*: CCL:G: CMO Analysis of a roB3LYP calculation using
Gaussian 09 and NBO 6
*Date*: Wed, 23 Sep 2015 04:03:39 -0400

Sent to CCL by: "Johannes Straub" [johannes.straub()
aci.uni-heidelberg.de]
Hey!
I already posted this problem in the NBO forum, but still got no reply to my
problem, so I thought I'll try it here on CCL.
I'm working with Gaussian 09 D.01 and NBO 6.0.
For my studies, I'd like to compare some particular orbital energies (d-Orbital
set) of two isomeric Fe(IV)-oxo complexes, to see, if there are any significant
differences.
(The two isomers show different reactivity in HAT reactions.)
We figured out that the CMO Analysis feature of NBO 6.0 might be very promising
for this task, because I can see which MOs are the ones built up by the
important Fe d- and O p-Orbitals.
I started using a normal uB3LYP calculation with Gaussian
"#p sp pop=(full,nbo6read) scrf=(pcm,solvent=acetonitrile) gfinput
gfoldprint 5d 7f def2tzvp ub3lyp scf=(tight,xqc)
..
$NBO plot print=3 file=L1Fe-e2-s1-bs3-nd-s-CMO-1 CMO archive $END"
I get the .31 and .37 files containing the NBOs and the corresponding CMO output
in the Gaussian output file, as expected. However, I was not able to completely
identify the d-Orbital set for both alpha- and beta-spin orbitals. (They don't
have the same MO number and are built up by NBOs very differently).
So, I thought, a similar roB3LYP calculation might help, because I would get
only one set of orbital eigenvalues and therefore only one set of NBO orbitals,
which makes it more easy to assign the important orbitals. However, after the
restricted oben shell SCF calculation, the NBO 6 module seems to split the MO
eigenvalues again into a different set of alpha and beta spin orbitals having
new, different eigenvalues. (At least I was able to identify all the d-orbitals
both in alpha and beta spin now)
What exactly is the NBO module doing in this step? Are the new eigenvalues
reliable for the comparison of orbital energies between two isomeric complexes?
Thank you!
Johannes