Electronic structure of CaCu2O3: Spin ladder versus one-dimensional spin chain

Quantum chemical calculations on embedded cluster models have been performed to extract accurate estimates of the magnetic coupling J and hopping parameters t of CaCu2O3. 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 Cu2O3 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=-4t(2)/U) is not justified in all cases.