Bridge function

The bridge functions are infinite series of irreducible diagrams $D_{i}$ :

B^{(2)}(r)=\rho ^{2}{\frac {1}{2}}D_{1}(r)+\rho ^{3}[D_{2}(r)+D_{3}(r)]+\rho ^{4}[...]+...

and

B^{(1)}(r)={\frac {1}{3}}B^{(2)}(r)+\rho ^{3}\left[{\frac {1}{6}}D_{2}(r)-{\frac {1}{12}}D_{3}(r)\right]+\rho ^{4}[...]+...

where $\rho$ is the density of the fluid.

Universality of the Bridge functional[edit]

For Rosenfeld's principle of the universality of the bridge functional see ^[1].