Subject: Gaussian98 frequency calculations using FREQ keyword

From: Connie Chang <[email-masked]>
Date: Wed, 30 Oct 2002 12:23:52 -0500

Hi all --

I have a question about the output from using the FREQ keyword.  I first
optimized the structure with OPT and then used FREQ to calculate the
normal modes.

In the output, where are the normal coordinate vectors and/or the
Hessian matrix?  I've found something that looks like it is a Hessian
matrix -- it's called the full mass weighted force constant matrix as
follows:

My question is 1) what are the elements of the force constant matrix.
Is it the "Frc consts"  or is it the elements below that under the X Y Z
heading for individual atoms?  Are they the same thing, but one is in a
vectorized form and the other in component form?

2) why are the force constants only accurate or shown to 2 sig figs?
Where or how can I get more digits out?

 Full mass-weighted force constant matrix:
 Low frequencies ---   -5.1861   -1.6047   -1.2255   -0.0066
0.0480    1.8398
 Low frequencies ---   20.1222   22.2472   32.0298
 Harmonic frequencies (cm**-1), IR intensities (KM/Mole),
 Raman scattering activities (A**4/AMU), Raman depolarization ratios,
 reduced masses (AMU), force constants (mDyne/A) and normal coordinates:

                     1                      2                      3
                    ?A                     ?A                     ?A
 Frequencies --    20.1068                22.2471                32.0298

 Red. masses --    12.0000                12.0000                12.0000

 Frc consts  --     0.0029                 0.0035                 0.0073

 IR Inten    --     0.0000                 0.0091                 0.0030

 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   6     0.01  -0.03   0.09     0.03   0.02   0.05     0.06   0.09
0.00
   2   6     0.01  -0.02   0.07     0.02   0.01   0.08     0.02   0.11
0.00
   3   6     0.00   0.00   0.11     0.00   0.00   0.03     0.08   0.08
0.00
   4   6     0.03  -0.06   0.08     0.05   0.03   0.03     0.06   0.07
0.00
   5   6    -0.01   0.02   0.07    -0.02  -0.01   0.08     0.02   0.11
0.00
   6   6    -0.01   0.03   0.09    -0.03  -0.02   0.05     0.06   0.09
0.00
   7   6     0.00   0.00   0.11     0.00   0.00  -0.01     0.09   0.05
0.00
   8   6     0.03  -0.05   0.09     0.05   0.03  -0.01     0.08   0.04
0.00
   9   6     0.04  -0.07   0.05     0.07   0.04   0.04     0.02   0.06
0.00
  10   6     0.02  -0.03   0.04     0.03   0.02   0.09    -0.01   0.10
0.00
  11   6    -0.03   0.06   0.08    -0.05  -0.03   0.03     0.06   0.07
0.00

Thank you!
Connie

---

From: "Stefan Fau" <[email-masked]>
Date: Wed, 30 Oct 2002 14:05:35 -0500

Hi Connie,

the shown piece of the output contains the
harmonic frequencies, other spectroscopic
data and then the vibrational modes in cartesian
coordinates (with respect to the "Standard
Orientation").

You can increase the number of decimals with
# ... freq(hpfreq)

You can tune the completeness of the output
of the links with IOPs:
# ... IOP(x/y=z)       with x,y,z integers
They are documented in the "programmers
reference" and maybe in the header of the
link1 source code (just read it with more,
less, or some editor).

Stefan
______________________________________________________________________
Dr. Stefan Fau                    |      [email-masked]
University of Florida             |     (352) 392-6714
Quantum Theory Project
2319 NPB #92, P.O.Box 118435
Gainesville, FL 32611-8435

---

From: Tom Sundius <[email-masked]>
Date: Wed, 30 Oct 2002 22:40:05 +0200 (EET)

Hi Connie,

If you want a more complete output, you should add p on the route card:
#p ...
After the list of frequencies and eigenvectors you will then get
the Hessian listed both in terms of internal coordinates and
in terms of cartesian coordinates (the units are, however, not the same
as those used in most NCA programs). Of these, the matrix expressed in
cartesian coordinates is the most useful one.

The archive part of the output (at the end of the log file) also contains
the Hessian in cartesian coordinates. If you look at it closely, you
can find a line that looks like this:

),SGV(H2)]\NImag=0\\0.05135282,0.,0.00000017,0.01887735,0.,0.56374193,

(this was from a MP2 calculation on the water molecule)
NImag=0 means there are no imaginary frequencies. After the double
backslash you have the Hessian in cartesian coordinates. The order of
the matrix elements is the same as in the output you get with the p
option (a triangular matrix).

     Best regards,

       Tom

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
+++ for we know in part, and we prophecy in part +++