Liu hard disk equation of state

The Liu equation of state for hard disks (2-dimensional hard spheres) is given by Eq. 1 of .

For the stable fluid:

$Z_v=\frac{1+{\eta }^2/8+{\eta }^4/18-4{\eta }^4/21}{(1-\eta {)}^2}$

where the packing fraction is given by $\eta =\pi \rho {\sigma }^2/4$ where $\sigma$ is the diameter of the disks.

The EoS for the stable fluid, liquid-hexatic transition region and hexatic:

$Z_h=Z_v+\frac{b_1\underset{1}{\overset{m}{\eta }}+b_2\underset{2}{\overset{m}{\eta }}}{(1-c\eta )}$