CCL:G: ab initio polarizability calculations?

[Amir Bernat <bernat#post.bgu.ac.il>]

Hello,

I just got this reply From the Gaussian help Email a few days ago:

In Gaussian09, the combination of Placzek invariants (a2, b2) used
to
compute the Raman scattering activity, depolarization ratios (polarized
and unpolarized) for each normal mode i, is as follows:  
a2_i = Sum_xy (1/9)*(dalpha_xx * dalpha_yy)
b2_i = Sum_xy (1/2)*(3*dalpha_xy * dalpha_xy - dalpha_xx * dalpha_yy)
where dalpha_xx = derivative the the polarizability with respect to the
ith normal mode.

Raman Activity = 45*a2_i + 7*b2_i
Depolar (P) = 3*b2_i/(45*a2_i + 4*b2_i)
Depolar (U) = 6*b2_i/(45*a2_i + 7*b2_i)

The a2 and b2 invariants are not individually printed during a
Freq=Raman calculation.  The polarizability derivatives for each
normal
mode can however be printed using IOp(7/33=1).  One could write a
script
which would extract these tensors, form the invariants and then combine
them according to your particular optical setup.  
The individual a2 and b2 invariants are however printed (labeled Alpha2
and Beta2, respectively) if Freq=ROA is requested.  This option is
much
more computationally demanding as the electric dipole - magnetic dipole
and electric dipole - electric quadrupole polarizability derivatives are
computed as well. 

Amir 

On Thu, Sep 6, 2012 at 6:59 PM, Bradley Welch bwelch5[a]slu.edu <owner-chemistry+*+ccl.net> wrote:
>
> Sent to CCL by: "Bradley   Welch" [bwelch5 _ slu.edu]
> Hey everyone,
>
> I've done a few polarizability calculations with Gaussian and other programs. One thing I've noticed is all these programs have to do multiple calculations to give you a polarizability. Is there a paper(or papers) that describes the general method of how these programs calculate polarizability? I'm assuming it has to consider the field in the x,y,z directions, and combinations of others, but I would like to figure out exactly how it does it. I'm not doing frequency dependent polarizability, only the static polarizability.
>
>
> Bradley Welch
> Saint Louis University.
>
>
>
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--

--
Amir Bernat
http://physweb.bgu.ac.il/~bernat/