Electronic and magnetic properties of electron-doped V 2 O 5 and NaV 2 O 5
Because of its narrow split-off conduction band, doping of V 2 O 5 leads to interesting strongly correlated electrons. We study the effects of doping on V 2 O 5 's electronic and magnetic properties, either by adding electrons compensated by an artificial homogeneous background, or a virtual crystal approximation (VCA), by changing the atomic number Z V , so as to keep charge neutrality, or by explicitly introducing Na as a dopant. The former two are considered as a way to simulate injected charge by gating, the latter occurs in the vanadium bronze NaV 2 O 5 . We also simulate Na 1 - x V 2 O 5 using a virtual crystal approximation by changing the atomic number 10 ≤ Z Na ≤ 11 . The differences in the band structure, which result from how the electrons added to the band are compensated by positive charge in the three models, are compared. The electronic band structures are calculated using the quasiparticle self-consistent Q S G W method including a lattice polarization correction and the local spin density functional method with Hubbard- U corrections (LSDA+ U ). For NaV 2 O 5 , the half-filling leads to a splitting of the up- and down-spin lowest d x y band. The spins are found to prefer an antiferromagnetic ordering along the chain direction. Other spin configurations are shown to have higher energy and the exchange interactions are extracted and compared with literature. The optical conductivities are calculated and compared with experiment. Similar results are found for simply doping the band compensated by a background or virtual crystal approximation. Yet, the position of the occupied bands depends on the method chosen for compensating the charge. The most realistic way to simulate gating in which the compensating charge is kept away from the V 2 O 5 layer is the VCA with varying Z Na . The splitting between the up- and down-spin bands depends on the filling. Furthermore, we find that below a certain concentration of about 0.88 electrons per V, the FM arrangement becomes preferable over the antiferromagnetic one. The magnetic moments then gradually decrease as we lower the filling of the split-off band.