Verlet modified

The Verlet modified (1980) (Ref. 1) closure for hard sphere fluids, in terms of the cavity correlation function, is (Eq. 3)

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle y(r) = \gamma (r) - A \frac{1}{2} \gamma^2(r) \left[ \frac{1}{1+ B \gamma(r) /2} \right]}

where several sets of values are tried for A and B (Note, when A=0 the HNC is recovered). Later (Ref. 2) (1981) Verlet used a Padé (2/1) approximant (Eq. 6) fitted to obtain the best hard sphere results by minimising the difference between the pressures obtained via the virial and compressibility routes:

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle y(r) = \gamma (r) - A \frac{1}{2} \gamma^2(r) \left[ \frac{1+ \lambda \gamma(r)}{1+ \mu \gamma(r)} \right]}

with Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle A= 0.80} , $\lambda =0.03496$ and Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \mu = 0.6586} .

References

1. Loup Verlet "Integral equations for classical fluids I. The hard sphere case", Molecular Physics 41 pp. 183-190 (1980)
2. Loup Verlet "Integral equations for classical fluids II. Hard spheres again", Molecular Physics 42 pp. 1291-1302 (1981)