Filename for the phonon modes file. This file is in plain text with the following format:
Version: # Version number (currently ignored)
Nmodes: # Number of modes in the file
Np: # Number of primitive cells in the supercell, used to generate the modes
Comment line
frequency: # Frequency of first mode (in atomic units)
# Normal mode eigenvector (for first atom)
# Normal mode eigenvector (for second atom)
… # repeated for all atoms in the unit cell
frequency: # Frequency of second mode
…
Note that the order of atoms has to be the same as in the input (or geometry) file.