Smearing Formulas for Density Matrices
  We report on the development of a systematic variational perturbation theory for the euclidean path integral representation of the density matrix based on new smearing formulas for harmonic correlation functions. As a first application, we present the lowest-order approximation for the radial distribution function of an electron in a hydrogen atom. 
Michael Bachmann, Hagen Kleinert, and Axel Pelster
cond-mat.stat-mech quant-ph