Electronic structure and exchange coupling in α′-NaV2O5

Band-structure calculations of the electronic structure of alpha'-NaV2O5 were performed using the linear muffin-tin orbital method within the local-density approximation (LDA). The results of the calculations were used to determine the parameters of an extended tight-binding model which describes the dispersion of the bands formed by V d(xy) orbitals and includes explicitly V d(xy)-Op(x,y) hopping terms. It has been found that the effective hopping between d(xy) orbitals of V atoms placed at the opposite ends of consecutive rungs of a ladder is comparable to the hopping along the leg of the ladder, which suppresses the dispersion of the upper pair of V d(xy) bands. The electronic structure of different models for the charge-ordered low-temperature phase of alpha'-NaV2O5 was studied using the LDA + U approach. The LDA + U ground-state energy was calculated and compared for in-line and zigzag charge order in different magnetic configurations. The set of effective exchange constants between V4+ magnetic moments was calculated by mapping to the ground-state energy of a localized Heisenberg model.