**HAL will be down for maintenance from Friday, June 10 at 4pm through Monday, June 13 at 9am. More information**

- Home

[...]

[...]

The magnetic properties of the octahedral cluster NpCl diluted in Cs2ZrCl6 crystal have been calculated using a first principle method, SO-CASPT2. The spin Hamiltonian parameters modeling the fourfold degenerate ground state are extracted from calculations according to a first principle procedure. The agreement with the model parameters issued from experimental EPR data is good. The spin and orbital contributions to the model parameters are evaluated. Calculations are compared to crystal field theory at the different steps of calculations: while this theory is a very good framework to explain the main magnetic behavior, it is shown that it is not able to render precisely all the small effects.

Sr2IrO4 is characterized by a large spin-orbit coupling, which gives rise to bands with strongly entangled spin and orbital characters, called J1/2 and J3/2. We use light-polarization dependent ARPES to study directly the orbital character of these bands and fully map out their dispersion. We observe bands in very good agreement with our cluster dynamical mean-field theory calculations. We show that the J1/2 band, the closest to the Fermi level EF , is dominated by dxz character along kx and dyz along ky. This is actually in agreement with an isotropic J1/2 character on average, but this large orbital dependence in k-space was mostly overlooked before. It gives rise to strong modulations of the ARPES intensity that we explain and carefully take into account to compare dispersions in equivalent directions of the Brillouin zone. Although the latter dispersions look different at first, suggesting possible symmetry breakings, they are found essentially similar, once corrected for these intensity variations. In articular, the pseudogap-like features close to the X point appearing in the nearly metallic 15% Rh-doped Sr2IrO4 strongly depend on experimental conditions. We reveal that there is nevertheless an energy scale of 30meV below which spectral weight is suppressed, independent of the experimental conditions, which gives a reliable basis to analyze this behavior. We suggest it is caused by disorder.

5d iridium oxides are of huge interest due to the potential for new quantum states driven by strong spin-orbit coupling. The strontium iridate Sr2IrO4 is particularly in the spotlight because of the so-called jeff = 1/2 state consisting of a quantum superposition of the three local t2g orbitals with – in its most simple version – nearly equal population, which stabilizes an unconventional Mott insulating state. Here, we report an anisotropic and aspherical magnetization density distribution measured by polarized neutron diffraction in a magnetic field up to 5 T at 4 K, which strongly deviates from a local jeff = 1/2 picture even when distortion-induced deviations from the equal weights of the orbital populations are taken into account. Once reconstructed by the maximum entropy method and multipole expansion model refinement, the magnetization density shows crossshaped positive four lobes along the crystallographic tetragonal axes with a large spatial extent, showing that the xy orbital contribution is dominant. The analogy to the superconducting copper oxide systems might then be weaker than commonly thought.

The monomer [Ce(COT)] and the dimer [Ce(COT)], with Ce(III) and COT = 1,3,5,7-cyclooctatetraenide, are studied by quantum chemistry calculations. Due to the large spin-orbit coupling, the ground state of the monomer is a strong mixing of σ and π states. The experimental isotropic coupling in the dimer was evaluated by Walter et al. to be J = -7 cm (with a Heisenberg Hamiltonian [Formula: see text]) with a small anisotropic coupling of 0.02 cm. The coupling between the two Ce(III) in the dimer is calculated using CI methods. The low energy part of the spectra are modeled by spin Hamiltonians. All spin Hamiltonians parameters are deduced from ab initio calculations. g factors are calculated for both the pseudodoublet of the monomer and the pseudotriplet of the dimer and their sign have been determined. The magnetic coupling in the dimer is rationalized by a model based on crystal field theory. The kinetic and exchange contributions arising from the different configurations to the isotropic and anisotropic couplings are evaluated. It is shown that the main contribution to isotropic coupling is kinetic and originates from the f-f interaction due to the large transfer integral between those orbitals. However, the f-f interaction plays a non-negligible role. The anisotropic coupling originates from the difference of exchange energy of states arising from the ff configuration and is, in no matter, related to the anisotropy of the local magnetic moments as already pointed by van Vleck for a fictitious s-p system. The analysis of the natural orbitals evidences a superexchange mechanism through a σ orbital of the bridging cycle favored by a local 4f/5d hybridization and that the δ type orbitals, both the HOMOs of the ligands and the virtual f orbitals of the cerium atoms play an important polarization role, and to a less extend the π type orbitals, the HOMOs-1 of the ligands, and the metal f orbitals.

The magnetic anisotropy parameters of a hexacoordinate trigonally elongated Ni(II) complex with symmetry close to D3d are measured using field-dependent magnetization and High-Field and High-Frequency EPR spectroscopy (D = +2.95 cm-1 , |E/D| = 0.08 from EPR). Wavefunction based theoretical calculations reproduce fairly well the EPR experimental data and allows analysing the origin of the magnetic anisotropy of the complex. Calculations on model complexes allows getting insight into the origin of the large increase in the axial magnetic anisotropy (D) when the complex is brought to a prismatic geometry with a symmetry close to D3h. 2

[...]

The density matrix renormalization group in chemistry and molecular physics: Recent developments and new challenges The Journal of Chemical Physics 152, 040903 (2020); https://doi. ABSTRACT Taking as an example the simple CH 3 radical, this work demonstrates the cooperative character of the spin-polarization phenomenon of the closed-shell core in free radicals. Spin polarization of CH σ bonds is not additive here, as spin polarization of one bond enhances that of the next bond. This cooperativity is demonstrated by a series of configuration interaction calculations converging to the full valence limit and is rationalized by analytic developments. The same phenomenon is shown to take place in those diradicals where spin polarization plays a major role, as illustrated in square planar carbo-cyclobutadiene C 12 H 4. The treatment of cooperativity represents a challenge for usual post-Hatree-Fock methods. Published under license by AIP Publishing. https://doi.

[...]

[...]

[...]

Spin-polarization effects may play an important role in free radicals and in the magnetic coupling between radical centers. Starting from restricted open-shell calculations, i.e. a closed-shell description of the non-magnetic core electrons, a low-order perturbation expansion identifies the spin polarization contribution to the energy of mono-radicals and to singlet-triplet energy differences in diradicals. Broken-symmetry (BS) single-determinant calculations introduce only a fraction of spin polarization effects, and in a biased manner, since BS determinants are not spin eigenfunctions. We propose a simple technique to correctly evaluate spin-polarization energies by taking into account the effect of spin-flip components of one-hole one-particle excited configurations. Spin-decontamination corrections is shown to play a non-negligible role in BS evaluation of bond energies. The importance of spin-decontamination is illustrated on cases for which spin polarization is the leading contribution to the singlet-triplet gap, what characterizes twisted conjugated double-bonds and disjoint diradicals.

[...]

[...]

Crystal field theory Crystal field parameters Méthodes basées sur la fonction d’onde Relativistic and correlated ab initio calculations Anderson mechanism Bleaney's model Photodissociation Single ion magnet Finite nucleus effects Single molecule magnets Polarization Negative ions Nuclear spin Magnetism in organic systems Magneto-resistive effects SPINTRONICS Ab initio calculation Imidazolium salt Excited states Determinants Molécules aimants Excitation energies Ground states Electron g-factor Modèle de Bleaney Anisotropy Magnétisme dans les systèmes organiques Lanthanides Electron paramagnetism Cooperative effect Paramagnetism Magnétisme moléculaire Electron spin Anisotropie magnétique Free radicals SYSTEMS Déplacements chimiques paramagnétiques Calculs ab initio relativistes et corrélés Calcul ab initio Double exchange model POLYMER Décontamination de spin Exact diagonalization Hamiltonien modèle Wave functions Ligand-field theory Molecular electronic states Calculs ab initio Paramètres du champ cristallin Magnetic anisotropy HIGH-SPIN Actinide Spin decontamination SUPERCONDUCTIVITY Spectroscopy Molecular magnetism Hyperfine coupling Pentagonal bipyramid Modèle de double échange Effets magnéto-résistifs Molecular magnet Potential energy surfaces Crystal-field theory and spin Hamiltonians MOLECULAR MAGNETIC-MATERIALS Paramagnetic chemical shifts Magnetic properties Lanthanide Spin Hamiltonian Basis sets Hyperfine structure Ab initio calculations Density functional theory Model hamiltonian MACROCYCLIC POLYARYLMETHYL POLYRADICALS Heavy fermions Coupled cluster calculations Spin-orbit interactions AB-INITIO Diagonalisations exactes Actinides Manganites Luminescence Electron paramagnetic resonance Complexes de métaux de transition Ionic liquid Exchange and superexchange interactions CLUSTERS Spectroscopie Bleaney Single-molecule magnets NMR Configuration interaction Configuration interactions Relativistic corrections Magnetism MECHANISM Electronic correlation Molecule-photon collisions Iodine Perturbation theory