ABINIT
Electronic-structure suite for periodic systems, with plane-wave ground-state calculations, density-functional perturbation theory, and many-body excited-state methods.
Where it fits
Phonons, dielectric response, electronic bands and systematic materials studies.
Limits and practical considerations
Response and many-body calculations introduce additional convergence parameters and cost.
Licensing and access
Open-source distribution; consult the official release licence and external-library terms.