Cavity correlation function

$y(r_{12})$ is the cavity correlation function, given by

$y(r)\equiv g(r)/e^{-\beta \mathrm{\Phi }(r)}$

where $g(r)$ is the pair distribution function, $\mathrm{\Phi }(r)$ is the pair potential, and $\beta =1(/k_{B}T)$, where $k_B$ is the Boltzmann constant.