The intermediate and spin-liquid phase of the half-filled honeycomb   Hubbard model
  We obtain the phase-diagram of the half-filled honeycomb Hubbard model with density matrix embedding theory, to address recent controversy at intermediate couplings. We use clusters from 2-12 sites and lattices at the thermodynamic limit. We identify a paramagnetic insulating state, with possible hexagonal cluster order, competitive with the antiferromagnetic phase at intermediate coupling. However, its stability is strongly cluster and lattice size dependent, explaining controver- sies in earlier work. Our results support the paramagnetic insulator as being a metastable, rather than a true, intermediate phase, in the thermodynamic limit. 
Qiaoni Chen, George H. Booth, Sandeep Sharma, Gerald Knizia, and   Garnet Kin-Lic Chan
cond-mat.str-el