  We investigate the half-filled Hubbard model on an isotropic triangular
lattice with the variational cluster approximation. By decreasing the on-site
repulsion $U$ (or equivalently increasing pressure) we go from a phase with
long range, three-sublattice, spiral magnetic order, to a non-magnetic Mott
insulating phase -- a spin liquid -- and then, for $U\lesssim6.7t$, to a
metallic phase. Clusters of sizes 3, 6 and 15 with open boundary conditions are
used in these calculations, and an extrapolation to infinite size is argued to
lead to a disordered phase at $U=8t$, but to a spiral order at $U\gtrsim 12$.
