Re: CCL:Electrostatic model for ordinary hydrogen bonds

 Heh, the "the disappearing hydrogen" is a fine technical point.
 However,
 the electrostatic effect of the HB would be a nice, round zero without the
 electrostatic parameters. **That** is the important effect of the HB. The
 disappearing hydrogen can be more fairly described as part of the
 force-field model, and is indeed a good way of taking the covalent part of
 the HB into account. Just like SHAKE is a good way of acknowledging that
 bonds exist between atoms without actually doing its QM.
 Regards,
 Arno Papazyan
 On Tue, 19 May 1998, Donald E. Williams wrote:
 >
 > 	There seems to be a widespread misunderstanding that an ordinary
 > hydrogen bond (say O-H...O) can be modeled with a purely electrostatic
 > potential by "dumping everything into electrostatic parameters".
 If anyone
 > knows of such a model, I would like to hear about it.
 > 	There is a parameterization called the "disappearing hydrogen"
 model of
 > the OHB.  In this model, electrostatics are included, but also (and very
 > importantly) the repulsion of the hydrogen atom is set to zero, quite a
 drastic
 > change from a normal hydrogen atom.  It is easily shown that the effect of
 > eliminating hydrogen repulsion is by far more important than the
 > electrostatics.
 >
 > >decompose an HB into its "electrostatic" and
 "covalent" contributions. An
 > >"ordinary" HB (OHB) has both electrostatic and covalent
 components, although
 > >it can be reasonably modelled by classical force fields by dumping
 everything
 > >into electrostatic parameters. An OHB can be neutral or charged. A
 charged
 >
 > -Donald Williams
 >
 > --
 > Dr. Donald E. Williams		email:dew01-0at0-xray5.chem.louisville.edu
 > Department of Chemistry
 > University of Louisville	phone:502-852-5975
 > Louisville, KY 40292		fax:  502-852-8149
 >
 >
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