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≲6.7t, 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≳12.
@article{arxiv.0711.0244,
title = {The Hubbard model on the triangular lattice: Spiral order and spin liquid},
author = {Peyman Sahebsara and David Sénéchal},
journal= {arXiv preprint arXiv:0711.0244},
year = {2008}
}