# CCL:G: Reproducing the Gaussian reported frequencies

*From*: "Aron Rogier Vandeputte"
<wachtebeekse/./hotmail.com>
*Subject*: CCL:G: Reproducing the Gaussian reported frequencies

Sent to CCL by: "Aron Rogier Vandeputte" [wachtebeekse%x%hotmail.com]
To obtain SCT-factors for a specific reaction, I need the frequencies and
eigenvectors at different points along the reaction path. To do this, I
performed an IRC calculation with the calcall option. In this way I got the
second derivative matrix at every point. I wrote the matrix (after I made it
symmetric) to Maple where I diagonalized it. The eigenvalues correspond to those
reported by Gaussian, but when I try to convert them to frequencies something
goes wrong.
Gaussian output:
----------------
All quantities printed in internal units (Hartrees-Bohrs-Radians)
The second derivative matrix:
cc2 hc3 hcc3 hc4 hcc4
cc2 0.05230
hc3 -0.00001 0.34915
hcc3 -0.00775 -0.00970 0.11675
hc4 -0.00001 0.00088 -0.00807 0.34923
hcc4 -0.00775 -0.00807 0.02445 -0.00967 0.11679
dih4 0.00000 0.00000 0.00000 -0.01504 0.04380
hc5 -0.00001 0.00088 -0.00807 0.00089 -0.00807
hcc5 -0.00775 -0.00313 0.06337 -0.00313 0.06332
....
Maple worksheet:
----------------
hartree:=4.35975E-18; Joule/Hartree
bohr:=0.52917725E-10: meter/bohr
amu:=1.660538E-27: kg/amu
hbar:=1.0545E-34:
for j from 1 to 21 do
if (Re(v[j])>0) then v[j] = j_th eigenvalue
FREQUENCY[j]:=evalf(Re(1/2/Pi*sqrt(v[j]*hartree/bohr**2/amu)/100/3E8));
fi;
od:
The strange thing is that there is no correlation between the frequencies that I
found and those produced by Gaussian. So, the fault can't be only caused by
wrong conversions. I wonder what I'm doing wrong: isn't this the correct matrix
for frequency calculation and how can I get the right one?
Thanks in advance,
Aron
wachtebeekse%%hotmail.com