You can use the ReaxFF / LAMMPS code, which has the functionality of frequency calculations. You can also take full numeric analysis code from other programs such as GAMESS if you are willing to deal with the coding. 

@Sean Nedd : Please elaborate. I want to do with LAMMPS this program.

thank you

I have used ReaxFF with its frequency analysis directly from the van Duin group. They have a version in LAMMPS accessible by pair_style reax/c

One site with further info is:

http://lammps.sandia.gov/doc/pair_reax_c.html

I do not use this version of ReaxFF, however if it's like the standalone ReaxFF code, the documentation for LAMMPS should explain how to access the frequency calculation functionality.