  We study the ground state properties of the geometrically frustrated Hubbard
model on the anisotropic checkerboard lattice with nearest-neighbor hopping $t$
and next nearest-neighbor hopping $t'$. By using the path-integral
renormalization group method, we study the phase diagram in the parameter space
of the Hubbard interaction $U$ and the frustration-control parameter $t'/t$.
Close examinations of the effective hopping, the double occupancy, the momentum
distribution and the spin/charge correlation functions allow us to determine
the phase diagram at zero temperature, where the plaquette-singlet insulator
emerges besides the antiferromagnetic insulator and the paramagnetic metal.
Spin-liquid insulating states without any kind of symmetry breaking cannot be
found in our frustrated model.
