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In quantum chemistry, single-reference Coupled Cluster theory, and its refinements introduced by Bartlett, has become a “gold-standard” predictive method for taking into account electronic correlations in molecules. In this article, we introduce a new formalism based on a Coupled Cluster expansion of the wave function that is suited to describe model periodic systems and apply this methodology to the case of hole-doped antiferromagnetic two-dimensional (2D)-square spin-lattices as a proof of concept. More precisely, we focus our study on 1/5 and 1/7 doping ratios and discuss the possible ordering effect due to large hole–hole repulsion. Starting from one of the equivalent single determinants exhibiting a full spin alternation and the most remote location of the holes as a single reference, the method incorporates some corrections to the traditional Coupled Cluster formalism to take into account the nonadditivity of excitation energies to multiply excited determinants. The amplitudes of the excitations, which are possible on the excited determinants but impossible on the reference, are evaluated perturbatively, while their effect is treated as a dressing in the basic equations. The expansion does not show any sign of divergence of the wave operator. Finally, the probabilities of holes moving toward the first- and second-neighboring sites are reported, which confirms the importance of the hole–hole repulsion and offers a picture of how stripes expand around its central line in the “stripe phases” observed in cuprates.

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The crystal field parameters are determined from first-principles calculations in the [An<sup>III</sup>(DPA)<sub>3</sub>]<sup>3-</sup> series, completing previous work on the [Ln<sup>III</sup>(DPA)<sub>3</sub>]<sup>3-</sup> and [An<sup>IV</sup>(DPA)<sub>3</sub>]<sup>2-</sup> series. The crystal field strength parameter follows the Ln(III) &lt; An(III) &lt; An(IV) trend. The parameters deduced at the orbital level decrease along the series, while J-mixing strongly impacts the many-electron parameters, especially for the Pu(III) complex. We further compile the available data for the three series. In some aspects, An(III) complexes are closer to Ln(III) than to An(IV) complexes with regard to the geometrical structure and bonding descriptors. At the beginning of the series, up to Pu(III), there is a quantitative departure from the free ion, especially for the Pa(III) complex. The magnetic properties of the actinides keep the trends of the lanthanides; in particular, the axial magnetic susceptibility follows Bleaney’s theory qualitatively.

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Actinide +IV complexes with six nitrates [AnIV(NO3)6]2− (An = Th, U, Np, and Pu) have been studied by 15N and 17O NMR spectroscopy in solution and first-principles calculations. Magnetic susceptibilities were evaluated experimentally using the Evans method and are in good agreement with the ab initio values. The evolution in the series of the crystal field parameters deduced from ab initio calculations is discussed. The NMR paramagnetic shifts are analyzed based on ab initio calculations. Because the cubic symmetry of the complex quenches the dipolar contribution, they are only of Fermi contact origin. They are evaluated from first-principles based on a complete active space/density functional theory (DFT) strategy, in good accordance with the experimental one. The ligand hyperfine coupling constants are deduced from paramagnetic shifts and calculated using unrestricted DFT. The latter are decomposed in terms of the contribution of molecular orbitals. It highlights two pathways for the delocalization of the spin density from the metallic open-shell 5f orbitals to the NMR active nuclei, either through the valence 5f hybridized with 6d to the valence 2p molecular orbitals of the ligands, or by spin polarization of the metallic 6p orbitals which interact with the 2s-based molecular orbitals of the ligands.

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With a lateral bisnaphtho-extended chemical structure, finite 7–13 carbon atom wide armchair graphene nanoribbons (7–13-aGNRs) were on-surface synthesized. For all lengths up to N = 7 monomer units, low-temperature ultrahigh vacuum scanning tunneling spectroscopy and spatial dI/dV maps were recorded at each captured tunneling resonance. The degeneracy of the two central electronic end states (ESs) occurs in a slowly decaying regime with N converging toward zero for N = 6 long 7–13-aGNR (12 bonded anthracenes), while it is N = 2 (4 bonded anthracenes) for seven carbon atoms wide armchair GNRs (7-aGNRs). The two end dI/dV conductance maxima of ESs are also shifted away from strictly two ends of the 7–13-aGNR compared to the 7-aGNR. Using the quantum topology graph filiation between finite length polyacetylene and 7–13-aGNRs wires, we show that this slow decay of 7–13-aGNR ESs is coming from the property of the topological Hückel band matrix that expels the ESs into its eigenvalue spectrum gaps to keep harmony in the core spectrum.

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This article follows earlier studies on the physical origin of magnetic anisotropy and the means of controlling it in polynuclear transition metal complexes. The difficulties encountered when focusing a magnetic field on a molecular object have led to consider the electric field as a more appropriate control tool. It is therefore fundamental to understand what governs the sensitivity of magnetic properties to the application of an electric field. We have already studied the impact of the electric field on the isotropic exchange coupling and on the Dzyaloshinskii–Moriya interaction (DMI). Here, we focus on the symmetric exchange anisotropy tensor. In order to obtain significant values of anisotropic interactions, we have carried out this study on a model complex that exhibits first-order spin–orbit coupling. We will show that (i) large values of the axial parameter of symmetric exchange can be reached when close to the first-order spin–orbit coupling regime, (ii) both correlated energies and wave functions must be used to achieve accurate values of the symmetric tensor components when the DMI is non-zero, and (iii) finally, an interferential effect between the DMI and the axial parameter of symmetric exchange occurs for a certain orientation of the electric field, i.e., the latter decreases in magnitude as the former increases. While DMI is often invoked as being involved in magneto-electric coupling, isotropic exchange and the symmetrical anisotropic tensor also contribute. Finally, we provide a recipe for generating significant anisotropic interactions and a significant change in magnetic properties under an electric field.

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Sujets

CLUSTERS Model hamiltonian Calculs ab initio Dzyaloshinskii-Moriya interaction MECHANISM Determinants Heptacoordination HIGH-SPIN Hyperfine structure Diagonalisations exactes MACROCYCLIC POLYARYLMETHYL POLYRADICALS Effective Hamiltonian theory Magnetic susceptibility Density functional theory Exact diagonalization Dynamical mean-field theory Bleaney's theory Décontamination de spin DOTA ligand Crystal field theory Finite nucleus effects Lanthanide Bleaney Crystal-field theory and spin Hamiltonians Ligand-field theory Relativistic corrections Anisotropie magnétique Actinide High pressure Magnetism in organic systems Model Hamiltonians Configuration interactions Divalent cobalt FOS Physical sciences Isotropic and anisotropic exchange Ab initio calculation Heavy fermions Electron spin Magnétisme moléculaire Déplacements chimiques paramagnétiques Hamiltonien modèle Lanthanides MOLECULAR MAGNETIC-MATERIALS Magnétisme dans les systèmes organiques Perturbation theory Double exchange model Ab initio calculations Bleaney's model Electronic structure Calculs ab initio relativistes et corrélés Electron paramagnetic resonance AB-INITIO Excitation energies Iridates Disordered Systems and Neural Networks cond-matdis-nn Binuclear compounds Imidazolium salt Magnetic properties Basis sets Actinides Covalency Free radicals Ionic liquid MOLCAS calculations Spin-orbit interactions Iodine Correlated relativistic ab initio calculations Dynamical mean field theory NMR Hyperfine coupling Exchange and superexchange interactions Electron g-factor Wave functions Crystal field parameters Cooperative effect Iridate Electronic correlation Excited states Magneto-resistive effects Magnetic anisotropy Complexes de métaux de transition First-order spin–orbit coupling Luminescence Electron paramagnetism Magnetism Anderson mechanism Metal-insulator transition Spin-orbit coupling Coupled cluster calculations Calcul ab initio Effets magnéto-résistifs Magnetic Susceptibility Ground states Anisotropy Modeling Manganites Configuration interaction Model Hamiltonian derivation Dzyaloshinskii–Moriya interaction Modèle de Bleaney

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