First-principles calculations of the local electronic and magnetic properties of Cu in La2-xBaxCuO4

K. Nagamine (RIKEN, Wako-shi, Japan; KEK, Japan), H. Li (RIKRN, Wakoshi, Japan), T.M. Briere (KEK-MSL, Tsukuba, Japan), T.P. Das (SUNY Albany, Albany, NY)

First-principles calculations of the electronic and magnetic properties of the La2CuO4 and Ba-doped La2-xBaxCuO4 systems with x approx. 0.125 are performed. The cluster procedure is adopted, in which the central atoms are treated with an all-electron basis and the remainder of the lattice is approximated with point charges. Both the Hartree-Fock (HF) and hybrid (combining both density functional exchange-correlation and HF exchange) methods are used in the calculations. Three different lattice structures are used, which include the pure La2CuO4 orthorhombic structure and the tilted LTO and LTT structures of La2-xBaxCuO4. For the pure system, the calculated electronic field gradient (EFG) is in agreement with experimental value and the magnetic hyperfine field is 28% larger than the experimental value (G. Q. Zheng, et al., Physica C 208, 339 (1993)). For the doped system, the hole-poor and hole-rich regions are considered separately. For the hole-poor region, the EFG is in rather good agreement with the experimental results(H. Tou, et al., J. Phys. Soc. Jpn. 61, 1477, (1992)), (K. Kumagai, et al., J. Phys. Soc. Jpn. 60, 1448, (1991)), (A. W. Hunt, et al., Phys. Rev. Lett. 82, 4300, (1999)), (K. Yoshimura et al., Hyperfine Interactions 79, 867 (1993)) and the hyperfine field is 24% larger than for experiment. For the hole-rich region, calculations assuming different spin states (0 or 1) are compared, and the the EFG results for the spin 0 state are in agreement with experiments; the corresponding results for the spin 1 state are much smaller. Study of the local lattice relaxation caused by Ba doping results in displacement of the nearest apical oxygen away from Ba by about 0.29 Å which is in the same direction as, but 70% larger than, results from XAFS measurements.(D. Haskel, et al., Phys. Rev. B. 61, 7055 (2000))

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