From m10!frisch@uunet.UU.NET  Sun Mar 14 10:26:38 1993
Message-Id: <9303142141.AA05900@relay1.UU.NET>
Date: Sun, 14 Mar 93 15:26:38 EST
From: m10!frisch@uunet.UU.NET (Michael Frisch)
Subject: Isotopic substitution on g92
To: chemistry@ccl.net


Louis Grace asked,
     
         As a reference for some benzenoid compounds I'm studying, I'm doing
    ab initio calculations (using Gaussian92) on benzene and benzene-d6.
    I've successfully run the benzene molecule, but when I try a frequency
    calculation on benzene-d6, g92 doesn't seem to like my input file.  It keeps
    giving me "Expecting floating point, found end of line."  Does anyone know
    the exact format of an input file for a frequency calculation with isotopic
    substitution (using the keyword, freq=readisotopes) under g92?  Also, my
    benzene molecule was built with a dummy variable in the center, and it is
    the first line in the z-matrix.  Do I just ignore this when putting in my
    isotopic masses?
     
The input for Freq=ReadIso consists of one line with the parameters
for the thermochemistry -- Temperature (Kelvin), Pressure (Atm), and
(starting with Gaussian 92 Revision D) optionally the scale factor to
apply to the frequencies.  Zero temperature or pressure defaults to
the standard values.  A zero scale factor defaults to the recommended
value of 1/1.12.  Omitting the scale factor or setting it to 1 leaves
the frequencies unchanged.

The masses are entered as integers, with one for each atom on a line
by itself.  Only real (i.e., non-dummy) atoms are specified, as the
integer values customarily used to refer to the isotopes.  The program
then uses the corresponding exact value -- for eaxmple, requesting a
mass of 18 for Oxygen causes the value 17.9915939 to be used.

Here's a complete input file for water frequencies with the isotopes
O18, D, and T.  A temperature of 100 Kelvin, 2 atmospheres pressure,
and the standard scale factor are also requested:

# rhf/sto-3g freq=readiso

water

   0   1
 O
 H,1,R2
 H,1,R2,2,A3

 R2=0.98940918
 A3=100.02691259

100.0 2.0 0.0
18
2
3

Note that the values printed for the frequencies are the unscaled
ones, even if the thermochemistry uses scaling.y

In versions of Gaussian 92 prior to Revision D, the scale factor cannot
(and should not) be specified.

Mike Frisch
frisch@lorentzian.com
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