Spin Gaps in a Frustrated Heisenberg Model forCaV4O9

I report results of a density matrix renormalization group (DMRG) study of a model for the two-dimensional spin-gapped system ${\mathrm{CaV}}_4{\mathrm{O}}_9$. This study represents the first time that DMRG has been used to study a two-dimensional system on large lattices, in this case as large as $24\times 11$, allowing extrapolation to the thermodynamic limit. I present a substantial improvement to the DMRG algorithms which makes these calculations feasible.