Gibbs ensemble

Here we have the N-particle distribution function (Ref. 1 Eq. 2.2)

${\mathcal {G}}_{(N)}(X_{(N)},t)={\frac {\Gamma _{(N)}^{(0)}}{\mathcal {N}}}{\frac {{\rm {d}}{\mathcal {N}}}{{\rm {d}}\Gamma _{(N)}}}$

where $\Gamma _{(N)}^{(0)}$ is a normalized constant with the dimensions of the phase space $\left.\Gamma _{(N)}\right.$.

$\left.X_{(N)}\right.=\{r_{1},...,r_{N};p_{1},...,p_{N}\}$

Normalization condition (Ref. 1 Eq. 2.3):

${\frac {1}{\Gamma _{(N)}^{(0)}}}\int _{\Gamma _{(N)}}{\mathcal {G}}_{(N)}{\rm {d}}{\mathcal {N}}=1$

it is convenient to set (Ref. 1 Eq. 2.4)

$\Gamma _{(N)}^{(0)}=V^{N}{\mathcal {P}}^{3N}$

where $V$ is the volume of the system and ${\mathcal {P}}$ is the characteristic momentum of the particles (Ref. 1 Eq. 3.26),

${\mathcal {P}}={\sqrt {2\pi m\Theta }}$

Macroscopic mean values are given by (Ref. 1 Eq. 2.5)

$\langle \psi (r,t)\rangle ={\frac {1}{\Gamma _{(N)}^{(0)}}}\int _{\Gamma _{(N)}}\psi (X_{(N)}){\mathcal {G}}_{(N)}(X_{(N)},t){\rm {d}}\Gamma _{(N)}$

Ergodic theory

Ref. 1 Eq. 2.6

$\langle \psi \rangle ={\overline {\psi }}$

Entropy

Ref. 1 Eq. 2.70

$S_{(N)}=-{\frac {k_{B}}{V^{N}{\mathcal {P}}^{3N}}}\int _{\Gamma }\Omega _{1},..._{N}{\mathcal {G}}_{1},..._{N}{\rm {d}}\Gamma _{(N)}$

where $\Omega$ is the N-particle thermal potential (Ref. 1 Eq. 2.12)

$\Omega _{(N)}(X_{(N)},t)=\ln {\mathcal {G}}_{(N)}(X_{(N)},t)$

References

1. G. A. Martynov "Fundamental Theory of Liquids. Method of Distribution Functions", Adam Hilger (out of print)