A unified view on various iterative approaches to the ground-state and finite temperature properties of quantum spin systems

We show that several iterative techniques, which were proposed for calculating ground-state properties of quantum models, can all be derived as the zero-temperature limit of a real-space quantum renormalization method. As a consequence, all these techniques are systematically improvable by a perturbative approach, and may be extended in a natural way to nonzero temperatures. (orig.)