Tarrach, R., 1948-Valentí i Vall, M. Roser2009-10-222009-10-2219900163-1829https://hdl.handle.net/2445/9768We present a very simple but fairly unknown method to obtain exact lower bounds to the ground-state energy of any Hamiltonian that can be partitioned into a sum of sub-Hamiltonians. The technique is applied, in particular, to the two-dimensional spin-1/2 antiferromagnetic Heisenberg model. Reasonably good results are easily obtained and the extension of the method to other systems is straightforward.3 p.application/pdfeng(c) The American Physical Society, 1990SuperconductorsMagnetismeSuperconductorsMagnetisminfo:eu-repo/semantics/article57979info:eu-repo/semantics/openAccess