  In a half-filled Hubbard model on a square lattice, the next-nearest-neighbor
hopping causes spin frustration, and the collinear antiferromagnetic (CAF)
state appears as the ground state with suitable parameters. We find that there
is a metal-insulator transition in the CAF state at a critical on-site
repulsion. When the repulsion is small, the CAF state is metallic, and a van
Hove singularity can be close to the Fermi surface, resulting in either a kink
or a discontinuity in the magnetic moment. When the on-site repulsion is large,
the CAF state is a Mott insulator. A first-order transition from the CAF phase
to the antiferromagnetic phase and a second-order phase transition from the CAF
phase to the paramagnetic phase are obtained in the phase diagram at zero
temperature.
