Accurate Determination of the Electronic Structure Parameters of the Spin Ladder Compounds SrCu2O3, Sr2Cu3O5 and CaCu2O3

Ab initio embedded cluster calculations have been employed to calculate a large number of electronic structure parameters of three different spin ladders, namely SrCu₂O₃, CaCu₂O₃ and Sr₂Cu₃O₅. Using the iterative difference dedicated configuration interaction methodology, magnetic couplings J and hopping amplitudes t are determined for first to fourth nearest neighbors. In addition, the four-body cyclic exchange J _ring is extracted and the direct exchange K, the neutral-ionic hopping integral t ₀ and the on-site repulsion U are calculated for first and second nearest neighbor copper ions. The substitution of these parameters in the pertubative superexchange relation J=2K−4t ₀²/U yields magnetic coupling parameters in close agreement with the variational estimates. The spin ladders can be considered as an interpolation between the one-dimensional (1D) spin chains and the 2D antiferromagnets. Hence, results are compared with similar parameters in the spin chain Sr₂CuO₃ and the two-dimensional antiferromagnet La₂CuO₄.