pair correlation length, \(\xi\)

in thin films
https://doi.org/10.1351/goldbook.P04397
A quantity which approximates to the @[email protected] associated with certain @[email protected] profiles of diffuse layers. \(\xi \) is defined as the separation between two interacting entities (molecules, @[email protected] 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 @[email protected], nor with the range (effective distance) of the @[email protected] (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]