Subject: Would you like to help me?

From: "Shuji Ye" <[email-masked]>
Date: Thu, 28 Feb 2002 16:32:37 +0900

Dear everyone,

 I am a new learner of Gaussian 98.  I have a difficulty in calculating the
force constants of larger molecules
using Gaussian 98. Though I can get the force constants for every mode in
the infrared spectra, I don't know how to transfer these constants into
bond stretching, angle bending and torsional force constants. For example, I
can get the following informations of the calculation of nitrate ion NO3(-1)
at B3LYP/6-311G(d) level. I want to know the force constants of bond
stretching N-O and angle bending O-N-O and torsional moting O-N-O-O.( The
intramolecular interaction potential has the form
V(intra)=V(stretch)+V(bend)+V(torsion). V(stretch)=1/2Kr(r-r0)^2,
V(bend)=1/2Ktheta(theta-theta0)^2, V(torsion)=Kphi(1-icos(2phi-phi0))

If you know how to do it or you are good at using Gaussian 98, would you
like to give me any advice?
It is appreciated for  your kind help.

 Sincerely yours

 Shuji Ye
 -------------------------------
Shuji Ye

Depertment of Chemical System Engineering,
Graduate School of Engineering
The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
 --------------------------------

  Raman scattering activities (A**4/AMU), Raman depolarization ratios,
  reduced masses (AMU), force constants (mDyne/A) and normal coordinates:
                      1                      2                      3
                     A1                     B2                     B1
  Frequencies --   716.4176               716.7829               844.0095
  Red. masses --    15.8585                15.8583                14.4084
  Frc consts  --     4.7956                 4.8004                 6.0473
  IR Inten    --     0.5951                 0.6005                23.6155
  Raman Activ --     0.0000                 0.0000                 0.0000
  Depolar     --     0.0000                 0.0000                 0.0000
  Atom AN      X      Y      Z        X      Y      Z        X      Y      Z
    1   7     0.00   0.00   0.26     0.00  -0.26   0.00     0.89   0.00 0.00
    2   8     0.00   0.00   0.48     0.00   0.63   0.00    -0.26   0.00 0.00
    3   8     0.00  -0.48  -0.35     0.00  -0.20   0.48    -0.26   0.00 0.00
    4   8     0.00   0.48  -0.35     0.00  -0.20  -0.48    -0.26   0.00 0.00
                      4                      5                      6
                    A1                     A1                     B2
  Frequencies --  1068.1719              1431.6263              1431.6450
  Red. masses --    15.9949                14.5209                14.5211
  Frc consts  --    10.7526                17.5350                17.5356
  IR Inten    --     0.0003               498.8348               498.9929
  Raman Activ --     0.0000                 0.0000                 0.0000
  Depolar     --     0.0000                 0.0000                 0.0000
  Atom AN      X      Y      Z        X      Y      Z        X      Y      Z
    1   7     0.00   0.00   0.00     0.00   0.00   0.86     0.00   0.86 0.00
    2   8     0.00   0.00   0.58     0.00   0.00  -0.40     0.00  -0.10 0.00
    3   8     0.00   0.50  -0.29     0.00   0.13  -0.17     0.00  -0.33 0.13
    4   8     0.00  -0.50  -0.29     0.00  -0.13  -0.17   0.00  -0.33  -0.13

---

From: Tom Sundius <[email-masked]>
Date: Thu, 28 Feb 2002 17:48:07 +0200 (EET)

> It is appreciated for  your kind help.

You cannot use Gaussian to transform an ab initio force field directly to
internal coordinates. But you can read the ab initio cartesian force field
> from the archive part of the output, or the checkpoint file (after you
have converted it from binary to ASCII) and input it to a normal coordinate
analysis program and then convert the ab initio force field to internal
coordinates or symmetry coordinates.

If you really want to calculate a molecular mechanics force field from the
ab initio force field, it is more complicated, but can be done
(see, for instance, K. Palmo, L-O Pietila and S. Krimm, J. Comput. Chem.
12, 385 (1991)).

     Greetings,

       Tom Sundius

Tom Sundius
University of Helsinki, Dept of Physical Sciences   phone +358-9-191 50672
P.O.Box 64, FIN-00014 Helsinki, Finland             fax   +358-9-191 50610