Equations of state for crystals of hard spheres

The stable phase of the hard sphere model at high densities is thought to have a face-centered cubic structure. A number of equations of state have been proposed for this system. The usual procedure to obtain precise equations of state is to fit computer simulation results.

Alder, Hoover and Young equation of state (face-centred cubic solid)

${\frac {pV}{Nk_{B}T}}={\frac {3}{\alpha }}+2.56+0.56\alpha +O(\alpha ^{2}).$

where $\alpha =(V-V_{0})/V_{0}$ where $V_{0}$ is the volume at close packing, $p$ is the pressure, $T$ is the temperature and $k_{B}$ is the Boltzmann constant.

Almarza equation of state

For the face-centred cubic solid phase (Eq. 19):

$p\left(v-v_{0}\right)/k_{B}T=3-1.807846y+11.56350y^{2}+141.6000y^{3}-2609.260y^{4}+19328.09y^{5}$,

where $\left.v\right.$ is the volume per particle, $v_{0}\equiv \sigma ^{3}/{\sqrt {2}}$ is the volume per particle at close packing, and $y\equiv (p\sigma ^{3}/k_{B}T)^{-1}$; with $\left.\sigma \right.$ being the hard sphere diameter.

Hall equation of state (face-centred cubic)

Eq. 13:

$z({\mathrm {solid} })-\left[(12-3\beta )/\beta \right]=2.557696+0.1253077\beta +0.1762393\beta ^{2}-1.053308\beta ^{3}+2.818621\beta ^{4}-2.921934\beta ^{5}+1.118413\beta ^{6}$

where

$\beta =4(1-v_{0}/v)$

$z(solid)={\frac {pV}{Nk_{B}T}}$

Speedy equation of state

(, Eq. 2)

${\frac {pV}{Nk_{B}T}}={\frac {3}{1-z}}-{\frac {a(z-b)}{(z-c)}}$

where

$z=(N/V)\sigma ^{3}/{\sqrt {2}}$

and (Table 1)

Crystal structure	$a$	$b$	$c$
hexagonal close packed	0.5935	0.7080	0.601
face-centred cubic	0.5921	0.7072	0.601
face-centred cubic	0.620735	0.708194	0.591663