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First-principles calculations are performed to investigate f magnetism in A 2 Ti 2 O 7 (A=Eu, Gd, Tb, Dy, Ho, Er, Yb) magnetic pyrochlore oxides. The Hubbard U parameter and the relativistic spin orbit correction are applied for a more accurate description of the electronic structure of the systems. It is argued that the main obstacle for the first-principles study of these systems is the multi-minima solutions of their electronic configuration. Among the studied pyrochlores, Gd 2 Ti 2 O 7 shows the least multi-minima problem. The crystal electric field theory is applied for phenomenological comparison of the calculated spin and orbital moments with the experimental data. [ABSTRACT FROM AUTHOR]

We use density functional theory to investigate effects of spin-orbit coupling and single-stripe-type antiferromagnetic (sAFM) ordering on the crystal structure and electronic properties of SmFeAsO. The results indicate that AFM ordering causes the crystal structure transition from tetragonal to orthorhombic, along with increase in the height of As atoms from Fe layer due to magnetostriction. It also leads to the opening of partial band gaps, the emergence of a prominent peak near Fermi energy (E F) in the density of states (DOS) and a reduction in Fermi surface nesting. The study finds a correlation between the calculated area under the DOS curve, spanning from E F to the first peak above it, and the optimal electron-doped concentration required for inducing superconductivity in SmFeAsO. The findings suggest that spin and charge density waves can play important roles in the superconducting mechanism of Fe-based superconductors. Our calculations demonstrate that spin-orbit coupling reduces electronic correlation. [ABSTRACT FROM AUTHOR]