Subject: Re: G: Gaussian Frequency calculation

From: "Jens Spanget-Larsen" <[email-masked]>
Date: Fri, 4 Jul 1997 11:06:00 +0100

Dale:

On 2 Jul 1997, you wrote: 07:36:12 -0700 (PDT)

> If you get a response to this question, please post it to the CCL or G; I
> am very interested in hearing the answer, as I have wondered about the
> validity of Rupert's claim myself.  I don't understand why people write
> their own routines to diagonalize the full force-constant matrix provided
> by G94, when it would be much simpler to just mass-weight the
> eigenvectors, and renormalize.

As you may have gathered from the postings on the G-list, the 
discussion is continuing.  It turns out that the 'proper' 
cartesian displacement coefficients are obtained from the printed 
G94 normal mode coefficients in the following way:

MULTIPLY THE PRINTED G94 NORMAL MODE COEFFICIENTS BY THE INVERSE
SQUARE ROOT OF THE REDUCED MASS 'M'. 

This produces the cartesian displacement vector X in 'real' x-space, 
that corresponds to a normal mode vector Q of unit length in 
abstract, mass-weighted q-space.  It is as simple as that, and you 
have the following relation between the length of the two vectors:
|Q| = sqr(M)|X|.

This, of course, should be well known by a lot of people (?), but I 
had to find it out by myself.  John Bertie <[email-masked]> 
has recently worked it all out in formal matrix algebra.

Another problem: You suggest a posting on the CCL, but my recent 
attempts to submit messages to CCL <[email-masked]> 
have been without effect: I get no mail error messages, but my 
messages don't appear on the list!  What may be wrong?

I am out of town for the next two weeks. 

Jens >--< 

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JENS SPANGET-LARSEN  
Department of Chemistry      Phone:  +45 46757781 + 2710
Roskilde University (RUC)    Fax:    +45 46757721 
P.O.Box 260                  E-Mail: [email-masked]
DK-4000 Roskilde, Denmark    http://frederik.ruc.dk/dis/chem/psos
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