Filip R. Vukajlović

DENSITY-FUNCTIONAL STUDIES OF THE ELECTRONIC STRUCTURE OF THE PEROVSKITE OXIDES : LA1-XCAXMNO3

Using density‐functional methods, we study the electronic structures of the lanthanum‐based ‘‘double‐exchange’’ perovskite magnets. Antiferromagnetic insulating solutions are obtained for both the end members, LaMnO3 and CaMnO3, within the local density approximation (LDA), with the Jahn‐Teller (JT) distortion of the oxygen octrahedron taken into account. The JT distortion splits off the Mn(3d)eg bands producing an energy gap within the LDA, with the bands derived from the (z2−1) orbital, pointed along the long basal‐plane Mn—O bond, occupied and the (x2−y2) bands empty. The on‐site Coulomb repulsion and the intra‐site exchange terms are found to be, respectively, U≂8–10 eV and J≂0.9 eV, from the ‘‘constrained’’ density‐functional theory. The large value of U as compared to the bandwidth indicates that the manganese perovskite oxides are strongly correlated systems.

Band structure of spin-Peierls cuprate CuGeO3

The spin-restricted and spin-polarized fully self-consistent linear muffin tin orbital band calculations for cuprate CuGeO3 are presented with Cu atoms in normal and displaced positions within the orthorhombic cells. This, computationally much cheaper, approach gives practically the same one-electron bands as recent linear augmented plane wave calculations, and the same qualitative explanation for the spin-Peierls transition observed at low temperatures in this compound. New self-consistent spin-polarized calculations of CuGeO3, for some supposed antiferromagnetic order in copper chains along the orthorhombic c axis, have given very small values for magnetic moments on Cu atoms. Again the dimerization of CuO2 chains can open a band gap at EF, if the Cu displacements in neighbouring chains are out of phase.

Magnetic moments of transition metals overlayers on fcc Ni surface

We calculate the magnetization profile in the (111) surface of face-centred cubic (fcc) Ni covered by a monolayer or a bilayer of 3d and 4d transition metals. The observed trends can be explained as in earlier works in terms of the hybridization between d states of the overlayer element and Ni substrate, although some interesting specific behaviour of the magnetization in the surface of fcc (111) Ni covered with different d metals has been observed.

Electronic structure and electric field gradient calculations for intermetallic compounds

Using the first-principles full-potential linear muffin-tin orbital method in the atomic sphere approximation, we have calculated the electronic structure of the intermetallic compound , and evaluated the electric field gradients (EFGs) at all of the three inequivalent positions (two Hf and one Fe) in its lattice. The main results extracted from the experimental investigations, concerning the different magnitudes and origins of the EFGs at inequivalent Hf sites, are correctly reproduced. The possible mechanisms of formation of the EFGs at these sites are analysed and discussed.

A comparative study of coulomb-correlated electronic structure of the spin-gapped compound α'-NaV2O5 in Pmmn and P21mn crystal structure

The paramagnetic, spin-polarized, and LDA+ U rotationally invariant, fully self-consistent linear-muffin-tin orbital band structure for the inorganic spin-gapped vanadate α ′ -NaV 2 O 5 has been calculated for both centrosymmetric group P m m n and noncentrosymmetric group P 2 1 m n (earlier assignment which is now denied as a room temperature structure) and twosupposed antiferromagnetic orders. A very small band gap solution and magnetic moments on vanadium atoms are obtained in the framework of local-spin-density functional approximation. The LDA+ U approach has produced the insulating antiferromagnetic solution with more appropriate energy gaps and magnetic moments. We found that the minimal crystal structure changes produce significant changes in the electronic structure and magnetic properties. Starting from an extended four-band tight-binding model, fitted to the paramagnetic P m m n bands, the hopping terms relevant for the calculation of exchange parameters of a spatially anisotropic Heisenberg mo...

Coulomb correlated band structure of one-dimensional SrCuO2

Abstract The spin-restricted, spin-polarized, and LDA + U fully self-consistent linear muffin-tin orbital band structure for the “one-leg ladder” compound SrCuO2 has been studied. An extremely small band gap solution with negligible magnetic moment on Cu sites is obtained in the framework of the LSDA method. On the other hand, the LDA + U method has produced the insulating antiferromagnetic solution with an energy gap of 1.63 eV and a magnetic moment of 0.89 μB. The standard LDA and LSDA SrCuO2 bands around the Fermi level are so similar to the recently discovered spin-Peierls inorganic compound CuGeO3 that one could perhaps expect the appearance of the same type of phase transition in orthorhombic strontium copper oxide SrCuO2.

Effect of adsorbed H atoms on magnetism in monoatomic Fe wires at Ir(100)

By means of ab initio calculations based on density-functional theory we demonstrate that magnetism in monoatomic Fe wires deposited on nanostructured Ir(100) surface can be tuned by their functionalization with hydrogen. The pristine monoatomic Fe wires deposited on nanostructured Ir(100) surface partially covered by H atoms are antiferromagnetic. However, the type of exchange interaction between Fe atoms can be changed by increasing H coverage. At fully hydrogenated Ir surface the Fe wires themselves are decorated with hydrogen, which gives rise to the ferromagnetic coupling between adjacent Fe atoms.