Subject: Re: CCL:Gaussian98W and hessian again....

From: "Jens Spanget-Larsen" <[email-masked]>
Date: Thu, 19 Dec 2002 08:44:34 +0100

Connie Chang:
 
>  I obtained the hessian from the archive portion of the output file
> starting from NImag=0|| and ending at ||.  I read this is as lower
> triangular matrix and filled in the blanks.  THen I converted it to
> units of erg/cm^2 and divided by the mass (my molecule contains all
> of the same atoms).  Then I diagonalize this matrix to get the
> eigenvalues and eigenvectors.  My question is -- Why don't the
> eigenvectors I get this way match the eigenvectors given by the
> output part of the file:
>                            6         7         8         9
>                           AG        BU        AG        BG
>        Frequencies ---   133.7777  217.8831  219.3526  220.1136
>
> etc.etc.?  I need the entire eigenvector matrix and not just 3*N-6
> translation/rotational modes.  The eigenvalues seem to match up
> fine, but the eigenvectors are different.  Am I somehow scrambling
> the atom order or something?

If I understand your procedure correctly, you obtain the normal modes 
in terms of mass-weighted displacement coordinates. But the 'normal 
modes' printed by Gaussian are expressed in cartesian displacement 
coordinates and normalized to unit length. - You may see the Gaussian 
web-place for further information.

Jens >--<  

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