Mean-square relative displacement in EXAFS
= Mean-square relative displacement in EXAFS
{title2=$\sigma^2=\langle[(\mathbf u_j-\mathbf u_0)\cdot\widehat{\mathbf R}]^2\rangle$}
The bond-direction <variance> of relative atomic displacement. A Gaussian distance distribution damps the coherent round-trip phase by $e^{-2k^2\sigma^2}$. Correlated atomic motion and static bond disorder contribute, so this is not generally a single atom's mean-square displacement about its lattice site.