Nguyen Van Hung, Nguyen Bao Trung, Le Hai Hung

Analytical expressions for the anharmonic effective potential, local force constant,
Displacement-displacement Correlation Function (DCF) CR and Debye-Waller factor described
by the Mean Square Relative Displacement (MSRD) sigma² and by the Mean Square Displacement
(MSD) u2of bcc crystals in the X-ray Absorption Fine Structure (XAFS) have been derived.
The effective interatomic potential of the system has been considered by taking into account the
influences of nearest atomic neighbors, and it contains the Morse potential characterizing the
interaction of each pair of atoms. Numerical results for u² , sigma² and CR of Fe and W are found to
be in good agreement with experiment. The ratios CR/u² and CR/sigma² approach constant values
at high temperatures showing the same properties obtained by the Debye model.