Phonon dispersion in Sr2RuO4 studied by a first-principles cumulative force-constant approach

The phonon frequencies along several high symmetry lines for Sr2RuO4 were calculated using the real-space cumulative force-constant approach. Except for the highest Delta(1) (xi 00) and Sigma(3) (xi xi 0) dispersions, all other 54 branches were quantitatively described very well, including the anomalous softening of the RuO6 octahedra rotational mode which was the lowest Sigma(3) dispersion along the (xi xi 0) direction. We did not see any imaginary phonon modes for Sr2RuO4 and demonstrated that the softening of the rotational mode of the RuO6 octahedra was not due to the anharmonic effects.