Ab Initio Fermi Surface Calculation for Charge-Density Wave Instability in Transition Metal Oxide Bronzes

The electronic structure of the charge density wave (CDW) bronze PO24WO32m, m 4, is determined using ab initio density functional theory. The calculation shows that the Fermi surface (FS) consists in the superposition of three one-dimensional FS’s associated with three types of chains. The q dependence of the electronic response function calculated from the electronic structure quantitatively accounts for the anisotropy of the fluctuations probed by x-ray diffuse scattering. The results validate the hidden nesting mechanism proposed for the CDW transitions in this series of bronzes. Because they exhibit a large variety of macroscopic quantum phenomena such as superconductivity, charge density wave (CDW), and spin density waves, lowdimensional metals are extensively studied [1]. The understanding of these phenomena requires nontrivial calculations of the electronic response, including the effect of electron-electron correlation and coupling of the conduction electrons with the lattice degrees of freedom. The layered transition metal oxide bronzes belong to these classes of metals. Superconductivity has been discovered in the AxWO3 (A Na and Rb) and WO32x tungsten bronzes, in the molybdenum purple bronze Li0.9Mo6O17, and very recently, CDW instabilities were observed in other Mo and W bronzes [2,3]. The general formula of bronzes is AxMyOz where A is a cation or an elemental group and MyOz a transition metal M oxide. The presence of Ax induces a partial filling of the bands formed by the transition metal dt 2g-orbitals. The bronzes provide a natural class of low-dimensional