Tight-binding based modeling to demonstrate metal-insulator transition in VO₂ within Mott-Hubbard picture

The mechanism of metal-insulator transition (MIT) in vanadium dioxide (VO₂) is still under debate whether it is due to the structural phase transition or electron correlations. A previous study, indicating that MIT appears far below the critical temperature of T_c ≈ 340 K when a small amount of oxygen is taken out from the system, suggested that oxygen screening and electronic correlations play a dominant role in MIT of VO2. To demonstrate how the Mott-Hubbard picture works in this mechanism, we construct a Hamiltonian with a kinetic part constructed within tight-binding scheme and an interaction part treated within the mean-field approximation for the system mimicking the situation of VO₂ without and with oxygen deficiencies. Keeping the Hubbard repulsion parameter, U, unchanged, we propose that the MIT is dominantly controlled by the changes of hopping parameters and the on-site energies due to possible orbital reorientations induced by correlation effects. We calculate the projected density of states (PDOS) using Green's function technique and demonstrate the opening/closing of the insulating gap within the Mott-Hubbard picture. Our results qualitatively reproduce the band renormalization picture inferred from the experimental data suggested by literature. In addition, we find that ferromagnetic electron spin configuration is necessary for the overall MIT scenario to work.