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Publisher: Cambridge : Royal Society of Chemistry × Subject: Quantum chemistry ×

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    Engineering Kitaev exchange in stacked iridate layers: Impact of inter-layer species on in-plane magnetism
    (Cambridge : Royal Society of Chemistry, 2019) Yadav, R.; Eldeeb, M.S.; Ray, R.; Aswartham, S.; Sturza, M.I.; Nishimoto, S.; Van Den Brink, J.; Hozoi, L.
    Novel functionalities may be achieved in oxide electronics by appropriate stacking of planar oxide layers of different metallic species, MOp and M′Oq. The simplest mechanism allowing the tailoring of the electronic states and physical properties of such heterostructures is of electrostatic nature - charge imbalance between the M and M′ cations. Here we clarify the effect of interlayer electrostatics on the anisotropic Kitaev exchange in H3LiIr2O6, a recently proposed realization of the Kitaev spin liquid. By quantum chemical calculations, we show that the precise position of H+ cations between magnetically active [LiIr2O6]3- honeycomb-like layers has a strong impact on the magnitude of Kitaev interactions. In particular, it is found that stacking with straight interlayer O-H-O links is detrimental to in-plane Kitaev exchange since coordination by a single H-ion of the O ligand implies an axial Coulomb potential at the O site and unfavorable polarization of the O 2p orbitals mediating the Ir-Ir interactions. Our results therefore provide valuable guidelines for the rational design of Kitaev quantum magnets, indicating unprecedented Kitaev interactions of ≈40 meV if the linear interlayer linkage is removed.
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    Self-assembly of endohedral metallofullerenes: A decisive role of cooling gas and metal-carbon bonding
    (Cambridge : Royal Society of Chemistry, 2016) Deng, Qingming; Heine, Thomas; Irle, Stephan; Popov, Alexey A.
    The endohedral metallofullerene (EMF) self-assembly process in Sc/carbon vapor in the presence and absence of an inert cooling gas (helium) is systematically investigated using quantum chemical molecular dynamics simulations. It is revealed that the presence of He atoms accelerates the formation of pentagons and hexagons and reduces the size of the self-assembled carbon cages in comparison with analogous He-free simulations. As a result, the Sc/C/He system simulations produce a larger number of successful trajectories (i.e. leading to Sc-EMFs) with more realistic cage-size distribution than simulations of the Sc/C system. The main Sc encapsulation mechanism involves nucleation of several hexagons and pentagons with Sc atoms already at the early stages of carbon vapor condensation. In such proto-cages, both Sc–C σ-bonds and coordination bonds between Sc atoms and the π-system of the carbon network are present. Sc atoms are thus rather labile and can move along the carbon network, but the overall bonding is sufficiently strong to prevent dissociation even at temperatures around 2000 kelvin. Further growth of the fullerene cage results in the encapsulation of one or two Sc atoms within the fullerene. In agreement with experimental studies, an extension of the simulations to Fe and Ti as the metal component showed that Fe-EMFs are not formed at all, whereas Ti is prone to form Ti-EMFs with small cage sizes, including Ti@C28-Td and Ti@C30-C2v(3).