Role of electronic correlations on the ground-state properties and on the pressure-induced metal-insulator transition inBaVS3

Abstract

We investigated the structural, magnetic and electronic properties of the hexagonal perovskite $\mathrm{Ba}\mathrm{V}{\mathrm{S}}_{3}$ by means of first-principles calculations within the density functional theory in the local spin density approximation (LSDA) that includes the Hubbard repulsion term $U\phantom{\rule{0.3em}{0ex}}(\mathrm{LSDA}+U)$ to take into account electronic correlations. We find that the $\mathrm{LSDA}+U$ scheme greatly improves on the LSDA results previously reported, and quantitatively accounts for all ground state properties found experimentally. First, the $\mathrm{LSDA}+U$ 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 $\ensuremath{\Delta}=47\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, which falls in the range of experimental values $(43\char21{}59\phantom{\rule{0.3em}{0ex}}\mathrm{meV})$, 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 $\mathrm{V}{\mathrm{S}}_{6}$ along the $c$-axis. We account for such three-dimensional conductivity in terms of the strong interaction between $V$ and $S$ orbitals within each $\mathrm{V}{\mathrm{S}}_{3}$ chain and between adjacent chains.