Subject: MOPAC6 FORCE DATA - PM3/AM1

From: Dave <[email-masked]>
Date: Mon, 15 Jan 1996 18:09:09 GMT

Could anybody out there throw some light on the derivation of the
various data output by the FORCE calculation under MOPAC?

The two values which I am puzzling over are the "T.DIPOLE" and 
"TRAVEL" values . What are the units of the numbers output? How do 
they relate to the Intensity of the band? Is the "TRAVEL" the change in 
 internal coordinates for the system?

Is the dipole calculated over x,y and z? I have found an equation for 
the 'true' integrated absorbtion coefficient which if of the form

A = Constant * (Freq**3) * (dipole(X)**2+dipole(Y)**2+dipole(z)**2)

Is this the form which should be used to calculate the intensity of the 
band?

Another book I have found expresses the integrated absorbtion 
coeffiecient in terms of the L-Matrix Values and the Change in dipole 
with change in 'internal coordinates'.

I am finding interpreting this part of the force calculation quite difficult 
and would welcome any clarification which people can offer relating to
which coordinate systems are being used and also how best to 
interpret the normal modes output.

Many thanks

David A. Tilbrook
[email-masked]
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David Tilbrook              *   Tel: 44 1483 300 800 x 9591
Polymer Group,              *                        x 2617
Chemistry Department,       *
University of Surrey,       *   Fax: 44 1483 259 514
Guildford, Surrey, GU2 5XH  *
U.K.                        *
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