Editing Liu hard disk equation of state

The '''Liu''' [[Equations of state | equation of state]] for [[hard disks]] (2-dimensional [[hard sphere model | hard spheres]]) is given by Eq. 1 of
<ref>[https://arxiv.org/abs/2010.10624]</ref>

:<math>Z = \frac{1 + \eta^2/8 + \eta^4/18- \4eta^4/21}{(1-\eta)^2} </math>

where the packing fraction is given by <math>\eta = \pi \rho \sigma^2 /4 </math> where <math>\sigma</math> is the diameter of the disks.
==References==
<references/>

[[Category: Equations of state]]