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

From: "Jens Spanget-Larsen" <[email-masked]>
Date: Thu, 19 Dec 2002 14:37:03 +0100

Dear Connie,

I elaborate a little bit:

If I understand your procedure correctly, you obtain the normal modes
Q in terms of mass-weighted displacement coordinates. Your normal mode
vectors should form an orthonormal set. But the "normal modes" printed
by Gaussian are expressed in cartesian displacement coordinates and
normalized to unit length (1 Angstrom). They are not necessarily
orthogonal.

You may try the following: 
First multiply the coefficients printed by Gaussian by the inverse 
square root of the reduced mass; the reduced mass is printed by 
Gaussian in units of u (or AMU, atomic mass unit). This produces the 
cartesian displacement vectors X associated with unit displacement 
along the corresponding normal coordinates Q. Then multiply the 
elements of X by the square roots of the pertinent atomic masses 
m(i). If my reasoning is correct, this should produce the proper 
normal modes Q in terms of mass-weighted displacement coordinates in 
units of sqr(u)*Angstrom. Hopefully, the resulting normal modes agree 
with the ones you have computed. 

Jens >--<

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
JENS SPANGET-LARSEN         Office:         +45 4674 2710
Department of Chemistry     Fax:            +45 4674 3011
Roskilde University (RUC)   Mobile:         +45 2320 6246
P.O.Box 260                 E-Mail:        [email-masked]
DK-4000 Roskilde, Denmark   http://virgil.ruc.dk/~spanget
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=