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

A series of accurate ab initio calculations on CupOq finite clusters. properly embedded in the Madelung potential of the infinite lattice, have been performed in order to determine the local effective interactions in the CuO2 planes of La2-xSrxCuO4 compounds. The values of the first-neighbor interactions, magnetic coupling (J(NN)=125 meV), and hopping integral (t(NN) = -555 meV) have been confirmed. Important additional effects are evidenced, concerning essentially the second-neighbor hopping integral t(NNN) = + 110 meV, the displace ment of a singlet toward an adjacent colinear hole, h(SD)(abc) = -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 values of the first-neighbor interactions. The dependence of J(NN) and t(NN) on 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 extended t-J model Hamiltonian has been proposed on the basis of these results. It is argued that the here proposed three-body effects may play a role in the charge/spin separation observed in these compounds, that is, in the formation and dynamic of stripes.