Electronic structure and magnetic properties of Li2ZrCuO4: A spin-1/2 Heisenberg system close to a quantum critical point

Based on density-functional calculations, we present a detailed theoretical study of the electronic structure and the magnetic properties of the quasi-one-dimensional chain cuprate Li2ZrCuO4 (Li2CuZrO4). For the relevant ratio of the next-nearest-neighbor exchange J(2) to the nearest-neighbor exchange J(1) we find alpha = -J(2)/J(1) = 0.22 +/- 0.02 which is very close to the critical point at 1/4. Owing this vicinity to a ferromagnetichelical critical point, we study in detail the influence of structural peculiarities such as the reported Li disorder and the nonplanar chain geometry on the magnetic interactions combining the results of local-density-approximation-based tight-binding models with LDA+U-derived exchange parameters. Our investigation is complemented by an exact diagonalization study of a multiband Hubbard model for finite clusters predicting a strong temperature dependence of the optical conductivity for Li2ZrCuO4.