# CCL:G: Hessian matrix in Cartesian coordinates by Gaussian.

*From*: "Roman D Gorbunov"
<rgorbuno---aecom.yu.edu>
*Subject*: CCL:G: Hessian matrix in Cartesian coordinates by
Gaussian.
*Date*: Fri, 13 Feb 2009 17:02:45 -0500

Sent to CCL by: "Roman D Gorbunov" [rgorbuno(0)aecom.yu.edu]
Dear CCL Subscribers,
I need to calculate the Hessian matrix in Cartesian coordinates.
I searched for the answer in the Interned found this:
http://www.ccl.net/chemistry/resources/messages/2005/10/03.007-dir/
It is written that first I have to calculate the checkpoint file.
Then I have to use "formchk name.chk name.fchk" to get a formated
file.
And finally I have to use a script called "demofc" to extract the
Hessian matrix given in the Cartesian coordinates.
I have a problem with the last step. I do not know how exactly should I use the
"demofc". I also cannot find any useful information about that.
Could anybody pleas help me with that?
By the way, I checked the formated checkpoint file (name.fchk). It contains some
information about the system, but I did not find there anything about Hessian
matrix. May be I have to put some additional keywords into the Gaussian input
file to force Gaussian to calculate the Hessian matrix?
Roman