Nonequilibrium Green's function approach to the pair distribution   function of quantum many-body systems out of equilibrium
  The pair distribution function (PDF) is a key quantity for the analysis of correlation effects of a quantum system both in equilibrium and far from equilibrium. We derive an expression for the PDF in terms of the single-particle Green's functions---the solutions of the Keldysh/Kadanoff-Baym equations in the two-time plane---for a one- or two-component system. The result includes initial correlations and generalizes previous density matrix expressions from single-time quantum kinetic theory. Explicit expressions for the PDF are obtained in second Born approximation. 
M. Bonitz, S. Hermanns, K. Kobusch, and K. Balzer
cond-mat.str-el