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Phonopy is an implementation of post-process phonon analyzer, which calculates crystal phonon properties from input information calculated by external codes, e.g., first-principles calculation code. Phonopy employs a real-space method. Phonopy calculates phonon frequencies from force constants. The force constants are obtained from atomic forces when an atom is slightly displaced in supercell (Parlinsk-Li-Kawasoe method).

In practice, phonopy provides automated pre- and post-processes to calculate the phonon properties, where crystal symmetry is fully included. In the pre-process, you can obtain supercells including displacements from your crystal structure.

Using Phonopy you can calculate atomic-forces using the supercells by your favorite calculator (e.g., WIEN2k or VASP). In the post-process, the atomic forces are collected and the phonon properties are calculated.

Force-constants interface is also prepared. If you can calculate force-constants directly, e.g., using DFPT in VASP, you don’t need to calculate atomic-forces, though you need a supercell, anyway.

Selected features are as follows:

Phonon dispersion relation (band structure)
Phonon DOS and partial-DOS
Phonon thermal properties, free energy, heat capacity, and entropy
Thermal expansion and heat capacity at constant pressure within quasi-harmonic approximation (phonopy-qha)