Re: CCL:van der Waals SURFACES/ELECTRON DEN

[Harald Svedung <svedung (- at -) phc.chalmers.se>]

Hi,
 I would just like to make a small comment on the side:
 The van der Waals size applies to a very simple picture of a molecular
 system. It is quite useful in many cases but (and this is my perhaps
 misdirected warning) when it comes to scattering processes, e.g.
 collisional energy transfer, the shape of the repulsive wall is of
 course important.
 How to go from electron density to the correct repulsive potential is
 discussed in e.g.:
 C. Nyeland, J. P. Toennies, Chem. Phys. 188 (1994) 205.
 There is also work in progress in this field.
 yours
 :-)         The spring has finally come here in Goeteborg!
 Harald
 On Tue, 25 Apr 2000, elewars wrote:
 > 2000 April 25
 >
 > Hello,
 >
 > I once read somewhere that an isosurface that encloses 97% of the total
 > electron density of a molecule corresponds best to the experimental van
 > der Waals surface.
 >
 > (1) Has anyone a reference to this, or to any percentage of the electron
 > density?
 > (2) Is it correct to say that the usual way to measure the "van der
 > Waals size" of a molecule is by X-ray diffraction (the molecules in a
 > crystal being considered to be in contact)?
 >
 > Thanks.
 >
 > E. Lewars
 > ======>
 >
 Harald Svedung (Ph.Lic.)                phone:          +46-31-7722816
 Department of Chemistry                 fax:            +46-31-167194
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