Entanglement and ground state level crossings in an extended Hubbard dimer

The single-site entanglement entropy in the ground state of an extended Hubbard dimer is calculated in terms of intrasite and intersite interaction parameters. Entanglement vanishes in a ferromagnetic regime characterized by a degenerate spin-polarized ground state. In parameter ranges with non-zero entanglement, the ground state is a linear combination of states with spin and charge modulation.