Exact ground state properties are presented by combining the exact diagonalization in the Fock space (including the long-range Coulomb interaction) with an ab initio optimization of the single-particle (Wannier) functions. The quasiparticle mass is almost divergent at the localization threshold, where the particle distribution of the Fermi-Dirac type gets smeared out. The analysis is performed using 1s-like Gaussian-type orbitals.

PACS numbers: 71.10.Fd, 71.10.Hf, 71.30.+h