2010/09/15 by M. Puig von Friesen, von Friesen, M. Puig, C. Verdozzi +3
Physics and Astronomy · #FOS: Physical sciences #Strongly Correlated Electrons (cond-mat.str-el) #cond-mat.str-el
paper · pdf · doi:10.48550/arxiv.1009.2917
2 pages, 1 figure
arxiv created 2010/09/15 · arxiv updated 2010/09/16
We use the Kadanoff-Baym equations within the framework of many-body perturbation theory to study the double occupancies in a Hubbard dimer. The double occupancies are obtained from the equations of motion of the single-particle Green's function. Our calculations show that the approximate double occupancies can become negative. This is a shortcoming of approximate, and yet conserving, many-body self-energies. Among the tested perturbation schemes, the T-matrix approximation is the only one providing double occupancies which are always positive.