From:	"Mr. Mingzuo Shen" <SHEN%CCQC <-at-> uga.cc.uga.EDU>
Date:	Mon, 04 Mar 91 13:22:07 EST
Subject:	Geometries predicted by various theoretical methods

Hello,

    I hope someone can help me or point to a reference on the
nature of predicted geometries by semi-empirical SCF methods
(such as MOPAC): that is, is a distance re (equilibrium distance),
or some sort of thermally averaged value?

    I know that ab initio methods give re, equilibrium values.

    I know that MM2 and MM3 give rg, usually called thermally
averaged nuclear distance. When a bond is more anharmonic,
(rg - re) is more positive. I found a reference on this sort of things:
K. Kuchitsu and S.J. Cyvin, Representation and experimental
determination of the geometry of free molecules. in "Molecular
Structures and Vibrations." S.J. Cyvin, ed. Elsevier (New York) 1972.
pp. 183-211.

     This article lists up to 8 different geometries. I wonder
what geometry the MOPAC predictions correspond to.

Thanks in advance for any help!

Mingzuo Shen

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