Other treatments of the problem include a mean-field numerical approach, as well as more recent treatments such as, also verifying the upper bound suggested above is a tight bound. Many Monte Carlo simulations were also performed, some of them in disagreement with the result quoted above. Few works deal with the quantum aspect of the problem. Classical Coulomb gap in clean system without disorder is well captured within Extended Dynamical Mean Field Theory (EDMFT) supported by Metropolis Monte Carlo simulations.