Subject: Reliability of the solvation models in GAUSSIAN

From: shochen michael <[email-masked]>
Date: Mon, 4 Aug 1997 14:28:24 +0300 (IDT)

Dear Netters

 In my current work I need to estimate oxidation potentials
for sevelal molecules. In other words, I need to calculate
the energy difference between ground state and cation-radical
(lowest doublet). I have experimental estimations of the oxidation
potentials for some of my compounds in water solution. All of my
molecules contain three sulfonic groups (SO3-), which of course are
ionized in water. Thus, I have as a ground state anionic species with
the charge -3, which do not exist in vacuum as systems with negative 
orbital enrgies of their HOMO (the oxidized form has the charge -2).
Vacuum calculations are irrelevant to my compounds, so I have used
a reaction field model implemented in GAUSSIAN-94 to simulate water
solution. I have used IPCM model with dielectric constant 80.
The level of quantum calculations was B3LYP/6-31G* (my molecules are very
big, so I can't use more extensive basis set with diffuse functions).
Unfortunately, for several cases I got very big (more than 1 eV)
difference between the calculated in my model and experimental values
of the oxidation potentials.
  My question is: How really are reliable the estimations of the solvation
effects in the IPCM model? Do somebody know references on examples
providing the comparison between theoretical and experimantal estimations
of solvation energies, or any physical values, which
are dependent on the solvation effects for the IPCM model ?

Thank you in advance.
Michael     
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Dr. Michael Shokhen
Senior researcher,
Department of Biochemistry,
G.S.Wise Faculty of Life Sciences,
Tel-Aviv University,
69978, Tel-Aviv, Israel.
Fax: 972-3-6415053
Email: [email-masked]

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