Electronic structure and exchange coupling in alpha '-NaV2O5

Band-structure calculations of the electronic structure of alpha'-NaV2O5 we re performed using the linear muffin-tin orbital method within the local-de nsity approximation (LDA). The results of the calculations were used to det ermine the parameters of an extended tight-binding model which describes th e dispersion of the bands formed by V d(xy) orbitals and includes explicitl y V d(xy)-Op(x,y) hopping terms. It has been found that the effective hoppi ng between d(xy) orbitals of V atoms placed at the opposite ends of consecu tive rungs of a ladder is comparable to the hopping along the leg of the la dder, which suppresses the dispersion of the upper pair of V d(xy) bands. T he electronic structure of different models for the charge-ordered low-temp erature 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 zig zag 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.