第一性原理计算及其应用II.ppt

第一性原理计算及其应用 II 万贤纲 南京大学物理学院 ccmp@nju.edu.cn July 02 2010 Contents MgB2研究 LDA+DMFT计算磁性相互作用 高温超导铜氧化物waterfall PuAm合金系统的RKKY作用和Kondo效应 高温超导铜氧化物的长程磁性相互作用 Contents MgB2压力研究 LDA+DMFT计算磁性相互作用 高温超导铜氧化物waterfall PuAm合金系统的RKKY作用和Kondo效应 高温超导铜氧化物的长程磁性相互作用 Magnetic Exchange interaction Magnetic materials is very useful Obtain a quantitative theory is important. Open new opportunities in computational design of new magnetic materials. Exchange interaction J Consider second-order change in the total energy related to the rotations of the magnetic moments appeared at sites and , and based on the magnetic force theorem and a linear response theory, the interatomic exchange constants can give by: Where and are the solutions of Hamiltonian (3). Systems mono-oxides MnO, FeO, CoO, NiO and high-Tc superconductor CaCuO2. (All these systems are Antiferromagnetic insulator with energy gap of a few eV and Neel temperature TN of a few hundred K.) LSDA fail to …, LDA+U … d electrons of transition metal elements are strongly correlated thus requiring DMFT. s and p electrons are weakly correlated and described by LDA. Coulomb interaction U and Hund’s exchange J were obtained by the constrained LDA calculation (Anisimov et al. (1991)) Experimental lattice Anderson impurity Solver Hartree Fock solution (LDA+U) Hubbard I (atomic self energy) Cluster Exact Diagonalization Solver: The cluster are chosen to include d orbital of transition metal ions hybridized with the p orbital of its nearest neighbor O atoms. (Fujimori et al. (1984)) Magnetic transition temperature Based on the obtained self-consistent results, we calculate the interatomic exchange parameters as the integral over the q space using (6,6,6) reciprocal lattice grid. Then use Monte-Carlo simulation to evaluate TN. Why TN decrease from NiO to MnO From MnO to NiO, the local magnetic moment increase. So if they have similar interatomic exchange parameters J, from MnO to NiO, the TN will