I found this paragraph from one of wiki article, "Mott considers a lattice model with just one electron per site. Without taking the interaction into account, each site could be occupied by two electrons, one with spin up and one with spin down. Due to the interaction the electrons would then feel a strong Coulomb repulsion, which Mott argued splits the band in two: The lower band is then occupied by the first electron per site, the upper by the second. If each site is only occupied by a single electron the lower band is completely filled and the upper band completely empty, the system thus a so-called Mott insulator." What I don't understood here is At first it is said that Mott consider a lattice model without taking interaction into account but later mentioned that due to interaction electorns would feel strong columb repulsion? Isn't that contradicts the first statement? It is first said that he considers just one electron per site but later said each site could be occupied by two electons, which again contradicts the first statement. So anyone please explain me what I'm missing here or what really affects metals to become insulators or what is mott insulators?