Influence of phonons on the pair distribution function deduced from neutron powder diffraction - art. no. 174302

The widths of the peaks in the pair distribution function (PDF) contain inf ormation on the phonons of a material. At large interatomic distances r the width of the peaks is fully determined by the thermal parameters. For low r, however, correlation effects reduce the width significantly, depending o n the shape of the phonon dispersion curves. We have studied the sensitivit y of the PDF with respect to the phonons by means of computer simulations b ased on various lattice dynamical models. The peak widths were calculated b oth in the one-phonon approximation as well as by a real space approach usi ng displacement correlation functions. Exemplary results are presented for Ni, Rh, Nb, Ge, and CaF2. We find that the PDF is rather insensitive to det ails in the phonon dispersion curves. Therefore, there is little hope to ex tract more information on the lattice vibrations from an experimental PDF t han is contained in the thermal parameters. This finding contradicts a clai m recently made by Dimitrov, Louca, and Roder [Phys. Rev. B 60, 6204 (1999) ].