On the electronic structure of the low lying electronic states of vanadium trioxide

The electronic structure of transition metal oxides is frequently studied using density functional theory. Nonetheless, the electronic structure of VO₃ has been found to be sensitive to the choice of functional. As a consequence, the basic question of whether or not the ground electronic state exhibits a Jahn-Teller distortion has yet to be resolved. Using basis sets of triple zeta quality and multireference configuration interaction wave functions as large as 700 million configuration state functions, we determine that the ground electronic state of VO₃ is a ²A₂ state in C_3v symmetry. The first two excited electronic states are also characterized and found to be the components of a degenerate ²E state, in C_3v symmetry, which exhibits a small Jahn-Teller distortion. The Jahn-Teller stabilization energy is only 40 cm⁻¹ and the barrier to pseudo-rotation is 9 cm⁻¹. This ²E state exhibits some unexpected properties. In the vicinity of the minimum energy conical intersection, the local topography appears almost quadratic, rather than linear, in the Jahn-Teller active coordinates. This gives rise to three symmetry-related seams of conical intersections in addition to the symmetry-required seam and results in the suppression of the geometric phase effect. These features, attributable to small linear Jahn-Teller parameters, are usually found in states characterized by e² (or e³e^′) electron configurations rather than the e³ configuration found here. In addition to its Jahn-Teller minimum, the first excited state exhibits a second minimum with a structure significantly distorted from C_3v. A conical intersection with C_s symmetry connects the two minima and puts an upper limit of 190 cm⁻¹ on the barrier connecting these minima.