Variational optimization of the 2DM: approaching three-index accuracy using extended cluster constraintsBrecht Verstichel, Ward Poelmans, Stijn De Baerdemacker, Sebastian Wouters and Dimitri Van NeckEur. Phys. J. B, 87 3 (2014) 59DOI: https://doi.org/10.1140/epjb/e2014-40788-x