Electronic structure ofCaCu2O3: Spin ladder versus one-dimensional spin chain

Abstract

Quantum chemical calculations on embedded cluster models have been performed to extract accurate estimates of the magnetic coupling $J$ and hopping parameters $t$ of $\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$. It is shown that this copper oxide compound is best described as a quasi-one-dimensional spin chain with weak interchain interactions within and between the ${\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$ planes. This magnetic structure is not reflected in the hopping parameters, since we find a large interplane hopping. Hence, the use of the simple second-order expression that relates $J$, $t$, and the on-site repulsion $U$ $(J=\ensuremath{-}4{t}^{2}∕U)$ is not justified in all cases.