  The 2D half-filled Hubbard model is studied by a nonperturbative analytic
theory of correlator projection. The original dynamical mean-field
approximation (DMFA) is reproduced at the first-order projection and then
improved by systematic inclusion of spatial correlations at higher orders. A
geometrical frustration induces a first-order Mott transition surface with a
finite-temperature critical end curve. Growth of antiferromagnetic correlations
gives single-particle spectra strongly modified from DMFA with shadow bands and
flat dispersions observed in high-T_c cuprates.
