The Heisenberg model on the 1/5-depleted square lattice and the CaV4O9   compound
  We investigate the ground state structure of the Heisenberg model on the 1/5-depleted square lattice for arbitrary values of the first- and second-neighbor exchange couplings. By using a mean-field Schwinger-boson approach we present a unified description of the rich ground-state diagram, which include the plaquette and dimer resonant-valence-bond phases, an incommensurate phase and other magnetic orders with complex magnetic unit cells. We also discuss some implications of ours results for the experimental realization of this model in the CaV4O9 compound. 
L. O. Manuel, M. I. Micheletti, A. E. Trumper and H. A. Ceccatto