Subject: CCL:D orbitals in Gaussian

From: "Joslyn Kravitz" <jyudenfr(at)umich.edu>
Date: Fri, 21 Nov 2003 13:59:03 -0500

Hello,

For some time I have been trying to use Gaussian to calculate the
molecular orbitals for some vanadyl compounds. I want to see which
atomic orbitals from the V are contributing to the homo, somo and lumo.
I have obtained lovely pictures of the MO's but I want to be able to
quantify the atomic orbital contributions. According to an e-mail I
received from the help line at Gaussian the orbitals are numbered like
this:

d0 = z^2 (really 3z^2-r^2)
d+1 = xz
d-1 = yz
d+2 = x^2 - y^2
d-2 = xy

Unfortunately, since Gaussian puts the molecules into the standard
orientation the atomic orbital names in the output no longer correspond
to the ones you normally think of based on symmetry. That is, you would
expect the dz^2 to be oriented along the V=O bond and all the others to
fall in place around it, but that doesn't seem to be true. The dz^2
orbital is oriented along whatever random direction is designated the z
axis in the "standard orientation" and then the other orbitals fall in
around that. Unfortunately, that makes interpreting the results a little
difficult, especially when different compounds are oriented differently,
so that the atomic orbitals are not named consistently between
compounds. 

I have tried using input coordinates that place the V=O bond along a
z-axis and setup the equatorial plane in an appropriate way and then
running a "NoSymm" calc, but that doesn't seem to help at all. Does
anyone know how I can convert my calculated orbitals to more "chemically
intuitive" ones, or at the very least, force Gaussian to not reorient
the molecule?
                       
Thank you,
Joslyn Kravitz
Depart. Of Chem.
University of Michigan