Dear David,

I'm using the scaled MM3 VdW-radii; the scaling is needed because the
functional form
of the VdW interactions in the MM3 (exp-C6 instead of the usual
Lennard-Jones) energy
expression. Because of this, the MM3 radii are 20% larger than "normal"
VdW radii.

For your system, you would then get:

  Radii
!
----------------------------------------------------------------------
! radii taken from Allinger et al. J.Mol.Struct.(THEOCHEM) 312 (1994)
69
! actual values used are MM3 radii divided by 1.2 and in Angstrom
!
! see also: J.Org.Chem. 70 (2005) 3542, [supporting information p. 49]
!
----------------------------------------------------------------------
     H = 1.350
     O = 1.517
     U = 2.100
  Subend

The good thing is that MM3 radii are available for almost the whole
Periodic Table,
and the radii are chosen consistently and from the same source.

Note also that the solvent radius is taken from experimental values
(macromolecular
density and molecular mass), and therefore, the choice is
"non-empirical". More
importantly, these choices seem to give good results.

!
-----------------------------------------------------------------------
! radius determined from macroscopic density (Rho,m)/molecular mass
(Mm),
! i.e. R**3 = 2.6752 * Mm * Rho,m
!
! parameters for water (rad in Angstrom)
!
-----------------------------------------------------------------------
   Solv eps=78.4 rad=1.9 emp=0.0
   Charged conv=1e-10 iter=1000 corr

On Mar 1, 2006, at 2:57 PM, Dave Sherman wrote:

> Actually, my last e-mail should read  "using the radii that Els
> provided...".  However if I used the intermediate U radius that Jonas
> proposed (1.698 Å), I  would have the same problems as at 2.05 and 1.0
> Å.  Regarding COSMO parameters, does anyone have a recommended
> reference?  I've done several literature searches but have not been
> successful.
>
> Thanks again!
>
> David M. Sherman
> Professor of Geochemistry
> Department of Earth Sciences
> University of Bristol
> Bristol BS8 1RJ UNITED KINGDOM
> Phone: 44-(0)117-954-5446
> http://mineral.gly.bris.ac.uk
>
>
––––––––––––––––––––––––––––––––––––––––––––
dr. Marcel Swart

Theoretische Chemie (kamer R152)
Vrije Universiteit Amsterdam
Faculteit der Exacte Wetenschappen

De Boelelaan 1083
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The Netherlands

T +31-(0)20-5987619
F +31-(0)20-5987629
E m.swart_at_few.vu.nl
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––––––––––––––––––––––––––––––––––––––––––––
Starting May 1, 2006:

ICREA researcher at
Institut de Química Computacional
Universitat de Girona

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Received on 2006-03-01 15:15:42