Electronic structure of theSr0.4Ca13.6Cu24O41 incommensurate compound

We extracted, from strongly-correlated ab-initio calculations, acomplete model for the chain subsystem of theSr0.4Ca13.6Cu24O41 incommensurate compound. Asecond neighbor t-J+V model has been determined as a function of thefourth crystallographic parameter , for both low and roomtemperature crystallographic structures. The analysis of the obtainedmodel shows the crucial importance of the structural modulations onthe electronic structure through the on-site energies and the magneticinteractions. The structural distortions are characterized by theirlong range effect on the cited parameters that hinder the reliabilityof analyses such as BVS. One of the most striking results is theexistence of antiferromagnetic nearest-neighbor interactions formetal-ligand-metal angles of 90. A detailed analysis of theelectron localization and spin arrangement is presented as a functionof the chain to ladder hole transfer and of the temperature. Theobtained spin arrangement is in agreement with antiferromagneticcorrelations in the chain direction at low temperature.