
Perturbation Theories for Molecular Fluids 225
Z =
6
πρ
ξ
0
1 −ξ
3
+3
ξ
1
ξ
2
(
1 −ξ
3
)
2
+3
ξ
3
2
(
1 −ξ
3
)
3
−
π
12
ρ
1 −ξ
3
i,j
x
i
x
j
l
ij
σ
2
ij
σ
i
+σ
j
+3σ
i
σ
j
ξ
2
1 −ξ
3
+
πρ
36
2
i,j,k
x
i
x
j
x
k
l
ij
l
ik
l
jk
σ
2
ij
σ
2
ik
σ
2
jk
, (8.35)
which reduces to the PY compressibility equation (7.84) for HS mixtures when l
ij
= 0
for every i and j. On the other hand, for a pure fluid of SHS, Equation 8.35 reduces to
Z =
1 +η +η
2
(
1 −η
)
3
−lη
1
(
2 +η
)
2
(
1 −η
)
2
+
l
3
η
2
36
. (8.36)
where
l =
1
1 −η
6 −τ +τη
−1
−
6 −τ +τη
−1
2
−6
1 +2η
−1
1
/
2
. (8.37)
Equation 8.36, which reduces to the PY compressibility equation (5.17) for a pure
HS fluid when l = 0, was first derived by Baxter (1968), who also derived the EOS
that arises from the ...