[Phonopy-users] Problem with setting nac_params with Phono3py API

[Thomas H. <tha...@gm...>]

I am attempting to use the Phono3py API to calculate the imaginary self
energy, phonon frequency, and phonon eigenvector arrays for further
analysis within a code. I'm using this for materials with optically active
phonons, so the NAC terms need to be present. At the moment, I'm following
the code in Si.py script in the examples folder:

primitive = phono3py.get_phonon_primitive()
nac_params = parse_BORN(primitive, filename="BORN")
nac_params['factor'] = Hartree * Bohr
phono3py.set_phph_interaction(nac_params=nac_params)
data = phono3py.get_phonon_data()

Since the set_phph_interaction is deprecated, I also tried:
phono3py.nac_params = nac_params
phono3py.init_phph_interaction()

In both of the above cases, the program works for GaAs, but there is no
apparent LO-TO splitting for the optical phonons at gamma (all optical
frequencies are the same), indicating that no NAC method was used. The
phono3py._interaction object has the nac_params correctly loaded within it.
Also, it appears that phono3py._interaction._dm has all the nac_params as
well. Then why is there no LO-TO splitting? Am I setting up the code
incorrectly, or what am I missing?