Lattice Dynamics of LaFeAsO_{1-x}F_{x} and PrFeAsO_{1-y} via Inelastic   X-Ray Scattering and First-Principles Calculation
  The lattice dynamics of LaFeAsO_{1-x}F_{x} (x=0, 0.1) and PrFeAsO_{1-y} (y~0.1) are investigated using inelastic x-ray scattering and ab-initio calculation. Measurements of powder samples provide an approximation to the phonon DOS, while dispersion is measured from a single crystal of PrFeAsO_{1-y}. A model that agrees reasonably well with all of the data at room temperature is built from results of ab-initio calculations by softening the strength of the Fe-As bond by 30%. 
T. Fukuda, A. Q. R. Baron, S. Shamoto, M. Ishikado, H. Nakamura, M.   Machida, H. Uchiyama, S. Tsutsui, A. Iyo, H. Kito, J. ...