$Sr_{14}Cu_{24}O_{41}$ : a complete model for the chain sub-system
Résumé
A second neighbor $t-J+V$ model for the chain subsystem of the $S\!r_{14}C\!u_{24}O_{41}$ has been extracted from ab-initio calculations. This model does not use periodic approximation but describes the entire chain through the use of the four-dimensional crystallographic description. The link between the parameters variations and the structural distortions have been discussed. This model allowed us to understand the origin of the chain dimerization and predicts correctly the relative occurrence of dimers and free spins. The orbitals respectively supporting the magnetic electrons and the holes have been found to be essentially supported by the copper $3d$ orbitals (spins) and the surrounding oxygen $2p$ orbitals (holes), thus giving a strong footing to the existence of Zhang-Rice singlets.