Ab initio phonon structure of h-YMnO3 in low-symmetry ferroelectric   phase
  We present a systematic first-principles study of the phonon spectrum of hexagonal YMnO3 in ferroelectric (multiferroic) phase. We investigated in detail the low-energy phonon modes, their dispersion, symmetry, as well as the infrared optical properties of the crystal and determined the phonon density of states. 
Konstantin Z. Rushchanskii and Marjana Le\v{z}ai\'c
cond-mat.mtrl-sci