From:	fredvc (+ at +) esvax.dnet.dupont.com
Date:	Fri, 1 Oct 93 16:29:56 -0400
Subject:	THE PARAMETRIC NATURE OF VDW RADII

Chris Cramer writes:

>>   van der Waals radii are not physical constants, they are parameters.
>>
>>   I make this point because I see a lot of modeling done which involves
>>taking the "van der Waals surface" and evaluating some property there. While
>>this particular property may have nothing to do with the physical
>>measurements which were used to develop the vdW radii from some OTHER
>>physical model, nevertheless they are justified as somehow being "better"
>>than parameters which are in fact optimized for EXACTLY the property being
>>studied.


	If anyone believes that VDW radii are "real", I urge them to take a look
at the original MMI paper [JACS, v89, p4345 (1967)]  Reasonalbe results were ob-
tained with a carbon vdw radius of ~1.7 Ang,....... and ~1.1 Ang!!

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                           FREDERIC A. VAN-CATLEDGE

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