Subject: G98, Solvation using the Onsager model.

From: Laurence Cuffe <[email-masked]>
Date: Fri, 11 May 2001 20:07:18 +0100

Dear All
Using the onsager model for solvation in g98 you are required to
input two parameters, the solvent dielectric constant and the 
molecular volume.  The molecular volume is generally derived from 
a gas phase calculation, and is determined, as I understand the 
code, by using a monte carlo procedure to sample the wave 
function.  It occurred to me that perhaps, it would be more 
appropriate to try and determine this by finding a self consistent 
value using the following procedure:
1)Calculate a volume for the gas phase molecule
2)Use this value in a new calculation to find a volume for the wave 
function of the solvated molecule.
3) repeat the above procedure until a consistent value was reached.
As a test molecule I took water with the O-H distance 1.05 
angstroms and the H-O-H angle 105.0 degrees.
Using HF and the default STO3G basis set
I got the following set of values:
Gas phase: recommended A0 2.46
1st solvated calc recomended A0 2.61
2nd solvated calc recommended A0 2.33
3rd solvated calc recomended A0 2.37
4th solvated calc recomended A0 2.46

Which leads to the question is step 2 valid?
if so what went wrong with step 3?
All the best
Laurence Cuffe