Elastic constants and phonon dispersion curves were calculated theoretically. A small value of the elastic constant C12 was explained by the volume dependent force acting on La atoms. Upon introducing a long range force between La atoms, phonon dispersion curves were obtained which were in good agreement with measured ones.

Theoretical Study of Lattice Dynamics in LaB6 and YbB6. Takegahara, K., Kasuya, T.: Solid State Communications, 1985, 53[1], 21-5