Symmetry adapted finite-cluster solver for quantum Heisenberg model in   two-dimensions: a real-space renormalization approach
  We present a quantum cluster solver for spin-$S$ Heisenberg model on a two-dimensional lattice. The formalism is based on the real-space renormalization procedure and uses the lattice point group-theoretical analysis and nonabelian SU(2) spin symmetry technique. The exact diagonalization procedure is used twice at each renormalization group step. The method is applied to the spin-half antiferromagnet on a square lattice and a calculation of local observables is demonstrated. A symmetry based truncation procedure is suggested and verified numerically. 
V.E. Sinitsyn, I.G. Bostrem, A.S. Ovchinnikov