Dear LAMMPS Users
I am trying to find vibrational modes and I need a force constant matrix, what command can I use to extract this information from my simulation?
I was reviewing the LAMMPS documentation and there is a dynamical_matrix command and a third_order command but they don’t exactly correspond to the information I require.
This kind of property is usually not computed from classical potentials, since often the equivalent data from quantum mechanical calculations is used as input to parameterize classical force fields.
In general, the second derivative of the potential energy with respect to displacements is not available, it needs to be approximated from finite differences and that is what the
dynamical_matrix command does. So if you need intermediate information, you have to modify that source code to output the properties you seek. Or create a modified command that directly outputs the data you are looking for and contribute it back.