Yukawa closure

The Yukawa closure relation for hard spheres is

$g_{ij}(r)\equiv h_{ij}(r)+1=0r<{\sigma }_{ij}=({\sigma }_i+{\sigma }_j)/2$

and

$c_{ij}(r)={\sum }_{n=1}\frac{K_{ij}}{r}{e}^{-z_{n}r}{\sigma }_{ij}<r$