## pair correlation length, $$\xi$$

in thin films
https://doi.org/10.1351/goldbook.P04397
A quantity which approximates to the @C00977@ associated with certain @N04262@ profiles of diffuse layers. $$\xi$$ is defined as the separation between two interacting entities (molecules, @M03667@ segments, ions, spins), either in bulk or interfacial regions, beyond which an appropriate function, referred to as pair correlation function, either decays (e.g. to $$\frac{1}{e}$$ of an 'initial' value) or vanishes. A characteristic length must be confused neither with the effective thickness of the @I03085@, nor with the range (effective distance) of the @I03098@ (pair) potential. This range is defined by the distance over which this potential and the corresponding correlation function both vanish.
Source:
PAC, 1994, 66, 1667. (Thin films including layers: terminology in relation to their preparation and characterization (IUPAC Recommendations 1994)) on page 1674 [Terms] [Paper]