There is a user-package called fix-phonon in LAMMPS.

(http://code.google.com/p/fix-phonon/). One need to install this package

before building LAMMPS. There are examples given and also the

documentation which tells you how to use it to calculate the dynamical

matrix, phonon dispersion curve etc..

I have used it to get phonon dispersion and map out soft phonon modes for

a model system of colloids with complex interactions. Now I want to

calculate the eigenvectors of the dynamical matrix to get the particle

displacements. For that I calculated the dynamical matrix at a q-value

where I am getting the soft modes. But, as I mentioned before, I don't

understand why it is a 4by8 matrix in stead of a 4by4 matrix. Do anybody

have any idea?

Chandana

Agreed - so if someone has such a package, please let