Eur. Phys. J. B 21, 375-381 (2001)
https://doi.org/10.1007/s100510170181

Ab initio determination of an extended Heisenberg Hamiltonian in CuO₂ layers

Laboratoire de Physique Quantique, IRSAMC, Université Paul Sabatier, 31062 Toulouse, France

Corresponding author: ^a calzado@cica.es

Received: 20 November 2000
Published online: 15 June 2001

Abstract

Accurate ab initio calculations on embedded Cu₄O₁₂ square clusters, fragments of the La₂CuO₄ 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 cm^-1 Å^-1.