Subject: Re: CCL:AIM in g98 problems - NO GOOD SOLUTION --- SUMMARY

From: "Dr. N. SUKUMAR" <[email-masked]>
Date: Fri, 23 Nov 2001 14:19:30 EST

Aren't bond orders a somewhat arbitrary concept?

The simplest -- and also cheapest -- way of estimating bond orders I know
of is simply to use a distance criterion and parametrize for different
bonds. Some molecular modeling software do just this. But calculating bond
orders ab initio? I'm afraid that really depends on how you define bond
orders.

More elaborate ways have been employed in the literature to calculate bond
orders, but really it depends on whose definition you accept (see, e.g.
J.S. Murray, N.Sukumar, S.Ranganathan and P.Politzer, “A Computational
Analysis of the Electrostatic Potentials and Relative Bond Strengths of
Hydrazine and some of its 1,1-Dimethyl Derivatives” Intl. J. Quantum Chem.
38, 611-629, 1990). I personally think that the bond order concept today
provides no more useful information than bond length or bond dissociation
energy, both of which can be unambiguously defined.

AIM can be used to determine the existence or absence of a bond path
between atoms in a molecule. It does not distinguish multiple bonds.

Dr. N. Sukumar
Rensselaer Department of Chemistry