Ab initio determination of an extended Heisenberg Hamiltonian in CuO2 layers

Details Ab initio determination of an extended Heisenberg Hamiltonian in CuO2 layers Ab initio determination of an extended Heisenberg Hamiltonian in CuO2 layers

2000-10-18

arxiv.org/abs/cond-mat/0010259v1

Physics

Condensed Matter

Strongly Correlated Electrons

11 pages, 5 figures, submitted to Phys. Rev. B

Scientific paper

10.1007/s100510170181

Accurate ab initio calculations on embedded Cu_4O_{12} square clusters, fragments of the La_2CuO_4 lattice, confirm a value of the nearest neighbor antiferromagnetic coupling (J=124 meV) previously obtained from ab initio calculations on bicentric clusters and in good agreement with experiment. These calculations predict non negligible antiferromagnetic second-neighbor interaction (J'=6.5 meV) and four-spin cyclic exchange (K=14 meV), which may affect the thermodynamic and spectroscopic properties of these materials. The dependence of the magnetic coupling on local lattice distortions has also been investigated. Among them the best candidate to induce a spin-phonon effect seems to be the movement of the Cu atoms, changing the Cu-Cu distance, for which the variation of the nearest neighbor magnetic coupling with the Cu-O distance is {\Delta J}/{\Delta d_{Cu-O}}\sim 1700 cm^{-1} A^{-1}.

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