Subject: Re: CCL:D orbitals in Gaussian

From: Joslyn Y Kravitz <jyudenfr:at:umich.edu>
Date: Tue, 25 Nov 2003 12:37:36 -0500 (EST)

I have received some helpful responses to my question about orienting
orbitals in Gaussian. The main suggestions had to do with symmetry, but
since my molecules are C1, that doesn't come into play. What does come
into play is the "NoSymmetry" keyword. This is not the same as
"GUESS=NoSymm" which has to do with the symmetry of the initial guess.
This "NoSymmetry" command tells Gaussian, "I don't care what you think the
major symmetry element is, I want my molecule to stay just the way I
entered it!" Or more formally, it prevents gaussian from putting the
coordinates into the standard orientation, so it uses the input
coordinates all the way through.

Thanks all,
Joslyn Kravitz

>===== Original Message From Joslyn Kravitz <jyudenfr:at:umich.edu> =====
>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