Isotopic effect on the local dynamics of crystalline germanium

The effect of isotopic mass difference on the local dynamics of crystalline germanium has been investigated by lattice dynamics calculation. The effect on the total, parallel and perpendicular mean-square relative displacements, as well as on the average bond distance, correlation and anisotropy of the relative atomic motion, has been calculated for the first three coordination shells. The isotopic differences are more pronounced where the relative atomic motion is more correlated. The agreement with recent high-quality EXAFS measurements provides evidence of the great potential of EXAFS in the study of the local dynamics of crystals.