Three-body forces in the lattice dynamics of some hcp metals

The consideration of paired interionic forces cannot explain the lattice dynamics of Be, Tb and Ho. In the present work, a phenomenological force constant model has been developed which considers three-body forces in addition to the usual forces of paired character. This approach explains the correct ordering of dispersion branches and the experimental degeneracy of the K-point in Be, Tb and Ho. Further good agreement is found between the theoretical curves and the neutron data of three high symmetry directions $\text{[0001], [01}\text{1}\text{0] and [11}\text{2}\text{0]}$ for all the three hcp metals.