Computes four approximations of B5 by FFT: HNC(C), HNC(V), PY(C), and PY(V).
HNC: hypernetted-chain integral-equation theory
PY: Percus-Yevick integral-equation theory
(V):virial (pressure) route
The HNC(V) approximation is equivalent to the "simple part" of the f-bond-only formulation of B5.
Expressions and values for individual diagrams agree with those of Kim, Henderson, and Oden (1966):
"Theory of Fluids and the Fifth Virial Coefficient", JCP 45(11).
Note that the expressions for B5HNC(C) and B5HNC(V) are reversed in the paper.
Diagrams are labeled using the nomenclature of Barker, Leonard, and Pompe (1966):
"Fifth Virial Coefficients", JCP 44(11); e.g., E5 is the five-membered ring.
X is added to the diagram name to denote if an x=r*df/dr bond is present. This our own nomenclature...