Central role of exchange-correlation hole in the 2D metal-insulator
  We show that the metal to insulator transition, whether generated by decreasing the electron density or by increasing the spin alignment, is determined by a universal functional form of the two-electron correlation function g(r). This result provides direct evidence of the central role of the Coulomb repulsion and exchange in driving the metal-insulator transition. 
J.S. Thakur and D. Neilson