Subject: how to calculate the solvation free energy calculation using PCM

From: "Asif Rahaman" <Arahaman(at)chemdept.chem.ou.edu>
Date: Wed, 28 Jan 2004 23:49:41 -0600

Dear CCLers:

   I am trying to calculate the solvation free energy for methane in water.
I have used Gaussian 03's PCM model.
   I get the following results:
 --------------------------------------------------------------------
 Variational PCM results
 =======================
 <psi(f)|H+V(f)/2|psi(f)>                     (a.u.) =     -40.533741
 <psi(f)|H+V(f)/2|psi(f)>                     (a.u.) =     -40.533856
 Total free energy in solution:
  with all non electrostatic terms            (a.u.) =     -40.522765
 --------------------------------------------------------------------
 (Polarized solute)-Solvent               (kcal/mol) =       -.07
 --------------------------------------------------------------------
 Cavitation energy                        (kcal/mol) =       9.98
 Dispersion energy                        (kcal/mol) =      -3.07
 Repulsion energy                         (kcal/mol) =        .06
 Total non electrostatic                  (kcal/mol) =       6.96
 --------------------------------------------------------------------

Now how do I cal calculate the solvation free energy from the above table?
Is it (<psi(f)|H+V(f)/2|psi(f)> - <psi(f)|H+V(f)/2|psi(f)>) or I have to 
perform the gas phase calculation and then subtract the gas phase energy 
> from the solution phase energy.

With best regards, Asif

I use the following input:

$ RunGauss
%NProc=4
%chk=ch4
%mem=64MB
# b3lyp/6-311g** opt pop=chelpg scrf=(pcm, solvent=water)

Methane B3LYP/6-311G**

0 1
C1
H1 1 b1
H2 1 b1 2 a1
H3 1 b1 2 a1 3 d1 1
H4 1 b1 2 a1 4 d1 1

b1 1.1
a1 109.5
d1 109.5

SAS
EPS=78.5
BONDI
DENSITY=1.000
TABS=298.0