Media type: E-Article Title: Variational perturbation theory for density matrices Contributor: Bachmann, Michael; Kleinert, Hagen; Pelster, Axel Published: American Physical Society (APS), 1999 Published in: Physical Review A, 60 (1999) 5, Seite 3429-3443 Language: English DOI: 10.1103/physreva.60.3429 ISSN: 1050-2947; 1094-1622 Keywords: Atomic and Molecular Physics, and Optics Origination: Footnote: