Cavity correlation function

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

$y(r)\equiv g(r)/e^{-\beta \Phi _{12}(r)}$

where $g(r)$ is the pair distribution function, $\Phi _{12}(r)$ is the pair potential, and $\beta =1(/k_{B}T)$, where $k_{B}$ is the Boltzmann constant.