Subject: PCM differences in G98 and G03

From: "Bachrach, Steven" <Steven.Bachrach~at~trinity.edu>
Date: Wed, 9 Jun 2004 15:18:01 -0500

We are trying to do some solvation calculations of anions using the PCM method and have run into the following unusual problem: G98 and G03 seem to give different results for identical systems.

For example, the formate anion at HF/6-31G* using PCM and the UAHF model

First the G98 results:

G-98

 Solvent: WATER
 Model  : PCM/UAHF, Icomp = 4
 Version: MATRIX INVERSION
 Cavity : PENTAKISDODECAHEDRA with  60 initial tesserae
 ------------------------------------------------------------------------------
 Nord Group  Hybr  Charge Alpha Radius            Bonded to
   1   CH    sp2   0.00   1.20  1.860     O3  [d]  O4  [d]
   3   O     sp3  -0.50   1.20  1.350     C1  [d]
   4   O     sp3  -0.50   1.20  1.350     C1  [d]
 ------------------------------------------------------------------------------

 -------------- VARIATIONAL  PCM  RESULTS -------------
 ------------------------------------------------------
    <Psi(0)| H |Psi(0)>        (a.u.) =   -188.182623
    <Psi(0)|H+V(0)/2|Psi(0)>   (a.u.) =   -188.302955
    <Psi(0)|H+V(f)/2|Psi(0)>   (a.u.) =   -188.304636
    <Psi(f)| H |Psi(f)>        (a.u.) =   -188.180236
    <Psi(f)|H+V(f)/2|Psi(f)>   (a.u.) =   -188.304688
    Total free energy in sol.
    (with non electrost.terms) (a.u.) =   -188.303733
 ------------------------------------------------------
    (Unpol.Solute)-Solvent (kcal/mol) =    -75.51
    (Polar.Solute)-Solvent (kcal/mol) =    -78.10
    Solute Polarization    (kcal/mol) =      1.50
    Total Electrostatic    (kcal/mol) =    -76.60
 ------------------------------------------------------
    Cavitation energy      (kcal/mol) =      6.66
    Dispersion energy      (kcal/mol) =     -8.15
    Repulsion energy       (kcal/mol) =      2.09
    Total non electr.      (kcal/mol) =      0.60
 ------------------------------------------------------
    DeltaG (solv)          (kcal/mol) =    -76.00
 ------------------------------------------------------

And now the G03 results

 Using the following non-standard input for PCM:
 scfvac
 radii=UAHF
 --- end of non-standard input.
 ------------------------------------------------------------------------------
 United Atom Topological Model (UAHF parameters set).
  Nord Group  Hybr  Charge Alpha Radius          Bonded to
    1   CH    sp2   0.00   1.20  1.860   O3   [d]  O4   [d]
    3   O     sp3  -0.50   1.20  1.350   C1   [d]
    4   O     sp3  -0.50   1.20  1.350   C1   [d]
 ------------------------------------------------------------------------------
 Polarizable Continuum Model (PCM)
 =================================
 Model                : PCM.
 Atomic radii         : UAHF (United Atom Topological Model).
 Polarization charges : Total charges.
 Charge compensation  : None.
 
 --------------------------------------------------------------------
 Variational PCM results
 =======================
 <psi(0)|   H    |psi(0)>                     (a.u.) =    -188.182625
 <psi(0)|H+V(0)/2|psi(0)>                     (a.u.) =    -188.300917
 <psi(0)|H+V(f)/2|psi(0)>                     (a.u.) =    -188.302699
 <psi(f)|   H    |psi(f)>                     (a.u.) =    -188.180456
 <psi(f)|H+V(f)/2|psi(f)>                     (a.u.) =    -188.302732
 Total free energy in solution:
  with all non electrostatic terms            (a.u.) =    -188.301754
 --------------------------------------------------------------------
 (Unpolarized solute)-Solvent             (kcal/mol) =     -74.23
 (Polarized solute)-Solvent               (kcal/mol) =     -76.73
 Solute polarization                      (kcal/mol) =       1.36
 Total electrostatic                      (kcal/mol) =     -75.37
 --------------------------------------------------------------------
 Cavitation energy                        (kcal/mol) =       6.66
 Dispersion energy                        (kcal/mol) =      -8.15
 Repulsion energy                         (kcal/mol) =       2.10
 Total non electrostatic                  (kcal/mol) =       0.61
 DeltaG (solv)                            (kcal/mol) =     -74.75
 --------------------------------------------------------------------

Both use the same keywords: SCRF=(PCM,SOLVENT=WATER), though G03 requires also the READ keyword and SCFVAC and RADII=UAHF at the end.

Anyone have a clue as to why the total free energies in solution and delaG(solvation) are different?

Thanks!

Steve

--
Steven Bachrach                                  ph: (210)999-7379
Department of Chemistry                        fax: (210)999-7569
Trinity University                              
1 Trinity Place
San Antonio, TX 78212
steven.bachrach~at~trinity.edu