Subject: Solvation in G92 - Try G94

From: <[email-masked]>
Date: Fri, 16 Jun 1995 16:23:00 -0400

> Could someone tell me how to take solvation effects into account in 
> Gaussian92, at the HF level.

I haven't carried out self-consistent reaction field calculations in G92 but I 
am carrying out a series of calculations using "SCRF=SCIPCM" option in G94 and 
this may be a good reason to upgrade.  Optimizations, frequencies, etc. are 
avilable for all HF and DFT methods.  Only single point energies are avialable 
for MP2 calaulations.  To date, I have had no difficulty with ground-state 
geometries but have run into some difficulties with transition-state 
calculations which I have communicated to Gaussian Inc.

In principal, SCRF=SCIPCM only requires an additional blank line plus a line 
with the dilectric constant to be used, in floating point format, after your 
geometry data, i.e., for water D=78.3:

     # 'Gaussian options' SCRF=SCIPCM
     (blank)
     Title
     (blank)
     'Charge' and 'multiplicity'
     'Geometry'
     (blank)
      78.3

Additonal parametres may also be entered on the same line as the dielectric 
value but only the dielectric need be specified.  The default parameters 
are probably best.  I was informed by Mike Frisch via Doug Fox, Gaussian 
Inc., that the additional parameters specify the isodensity contour value 
(0.0004 is recommended), the number of points for the Lebedev grid (default 
is 302), and various options which control how the linear equations are 
solved plus other details.  Mike also suggested:

     "You can certainly set down the number of integration points in SCIPCM...
     if you like.  Try

     78.3 0.0004 194 0

     to use a 194 point Lebedev grid on each atom.  Using a single integration 
     origin:

     78.3 0.0004 302 0 2

     This speeds up the calculation but is only correct for convex cavities. 
     (the default for the fifth parameter is 3, meaning a separate integration 
     grid around each atom).  You can also force inversion of the matrix instead
     of iterative solution of the linear equations:

     78.3 0.004 302 0 3 T

     This is faster for small-medium systems but very memory intensive and 
     slower for big systems."

My thanks to Mike Frsich and Doug Fox.

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| Karl F. Moschner, Ph. D.                                              | 
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