Proposal of an extended t-J Hamiltonian for high-T-c cuprates from ab initio calculations on embedded clusters - art. no. 214520

A series of accurate ab initio calculations on CupOq finite clusters. prope rly embedded in the Madelung potential of the infinite lattice, have been p erformed in order to determine the local effective interactions in the CuO2 planes of La2-xSrxCuO4 compounds. The values of the first-neighbor interac tions, magnetic coupling (J(NN)=125 meV), and hopping integral (t(NN) = -55 5 meV) have been confirmed. Important additional effects are evidenced, con cerning essentially the second-neighbor hopping integral t(NNN) = + 110 meV , the displace ment of a singlet toward an adjacent colinear hole, h(SD)(ab c) = -80 meV, a non-negligible hole-hole repulsion V-NN-V-NNN = 0.8 eV, and a strong anisotropic effect of the presence of an adjacent hole on the val ues of the first-neighbor interactions. The dependence of J(NN) and t(NN) o n the position of neighbor hole(s) has been rationalized from the two-band model and checked from a series of additional ab initio calculations. An ex tended t-J model Hamiltonian has been proposed on the basis of these result s. It is argued that the here proposed three-body effects may play a role i n the charge/spin separation observed in these compounds, that is, in the f ormation and dynamic of stripes.