Theoretical Model for Asymmetry Parameter
In 1993, Frenkel and Rehr derived expressions for EXAFS cumulants in a two-body perturbed harmonic oscillator and related them to thermal expansion (Phys. Rev. B 48, 585)
Rewritten in terms of the radial asymmetry paramater, their expressions become:
Our zero-point value for the radial asymmetry parameter of the nearest-neighbor interaction in copper (0.012 + 0.008) is consistent with the value calculated from their expressions (0.009)
For the nearest-neighbor bond in iodine, the expression for the radial asymmetry parameter contains only one parameter not easily found in the literature: the zero-point anharmonicity. Thus, our measurements can be used to estimate this value.