First order Mott transition at zero temperature in two dimensions:   Variational plaquette study
  The nature of the metal-insulator Mott transition at zero temperature has been discussed for a number of years. Whether it occurs through a quantum critical point or through a first order transition is expected to profoundly influence the nature of the finite temperature phase diagram. In this paper, we study the zero temperature Mott transition in the two-dimensional Hubbard model on the square lattice with the variational cluster approximation. This takes into account the influence of antiferromagnetic short-range correlations. By contrast to single-site dynamical mean-field theory, the transition turns out to be first order even at zero temperature. 
Matthias Balzer, Bumsoo Kyung, David S\'en\'echal, A.-M. S. Tremblay   and Michael Potthoff