Role of electronic correlations on the ground-state properties and on the pressure-induced metal-insulator transition in BaVS3

We investigated the structural, magnetic and electronic properties of the hexagonal perovskite BaVS3 by means of first-principles calculations within the density functional theory in the local spin density approximation (LSDA) that includes the Hubbard repulsion term U (LSDA+U) to take into account electronic correlations. We find that the LSDA+U scheme greatly improves on the LSDA results previously reported, and quantitatively accounts for all ground state properties found experimentally. First, the LSDA+U predicts an orthorhombic structure and a quasi-metallic ground state with a long-range antiferromagnetic (AFM) order in the quasi-hexagonal ab-plane, ferromagnetically (FM) coupled along the c-axis. Second, we studied the stability of competing crystal structures and competing magnetic orderings in terms of exchange integrals. The results account well for the experimental pressure-dependence of the metal-insulator transition and for the chemical-pressure induced AFM-FM transition reported recently in Sr-substituted samples. In particular, at the experimental value of the volume, V, we obtain an energy gap Delta=47 meV, which falls in the range of experimental values (43-59 meV), while, at smaller V values, we find an AFM-FM transition, in agreement with the above effects of Sr-induced chemical pressure. Finally, in the metallic phase, we find a nearly isotropic electrical conductivity, in agreement with experiments, despite the presence of quasi-one-dimensional chains of VS6 along the c-axis. We account for such three-dimensional conductivity in terms of the strong interaction between V and S orbitals within each VS3 chain and between adjacent chains.