The structure of the bulk and the (001) surface of V₂O₅. A DFT+U study

GGA (PW91) + U is applied to the calculation of the structure (lattice parameters) and the electronic structure of the V₂O₅ bulk and its (001) surface for different values of U_eff used in the literature (0.0, 3.0 and 6.6 eV). Similar surface lattice parameters are calculated for the (001) surface and for the bulk, as well as similar electronic structures. The calculated lattice parameters (a and b for the surface and a, b and c for the bulk) are in good agreement with experimental results. It seems that there is no strong correlation between the calculated lattice parameters and the value of U_eff. The calculated width of the valence band keeps the value of $\approx 5eV$ for the three studied U_eff. However, the energy gap between the valence and the conduction bands increases with the value of U_eff. U_eff = 3.0 eV seems to be the most adequate value to describe the energy gap after comparison with experimental results. Electronic density contour plots indicate that for a larger (smaller) U_eff the accumulated charge in the V-O(1) bond is overestimated (underestimated). The contour plots (in the a direction) show that the charge distribution V-O(3) is less correlated with U_eff than the charge distribution V-O(1), whereas charge distribution V-O(2) seems not to be corretaled with U_eff. The energy gap between the valence and the conduction bands seems to be strongly related with the charge distribution in the V-O(1) bond. The V-O(1) bond stability seems to be correlated with U_eff. However, the stability of the V-O(2) and V-O(3) bonds seems not to be strongly affected by U_eff. (paper)