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Stability of atomic structure and magnetic ordering of low-dimensional nanostructures with multiple non-equivalent sublattices

Stability of atomic structure and magnetic ordering of low-dimensional nanostructures with multiple non-equivalent sublattices

09 June 2017 

Ap/ B-607

p.m 3 h.

Pavel V. Avramov

Kyungpook National University, Daegu, South Korea

Stability of atomic structure and magnetic ordering of low-dimensional structures is the key point since the discovery of 1- and 2D nanowires, nanotubes, one-atom thick films (e.g. graphene and h-BN) and complex low-dimensional heterostructures. The great progress to describe and interpret the structure and properties of low-dimensional nanostructures has been achieved by electronic structure calculations of perfect 1D and 2D infinite crystalline lattices, for which an implementation of periodic boundary condition approximation can cause artificial structural stabilization. There are several basic mechanisms of structural and magnetic order instability of low-dimensional structures. In particular, quantum destabilization of atomic structure of low-dimensional nanoclusters with multiple non-equivalent sublattices can be caused by translation symmetry breakdown, for example in the case of fluorine-terminated graphene, h-BN and h-SiC narrow zig-zag nanoribbons with non-equivalent sublattices. The asymmetry of nanoribbon edges causes a uniform nanoribbon curvature with considerable out-of-plane bending of the ribbons, which results in breakdown of translational periodicity. Another mechanism of translational symmetry breakdown in low-dimensional carbon pentagon-constituted nanostructures with multiple sp2/sp3 sublattices was studied by electronic structure calculations. It was found that finite nanoclusters suffer strong uniform unit cell bending followed by breaking of crystalline lattice linear translation invariance. At one-electron level of theory, a perfectly flat lattice is just a regular point on a potential energy surface with non-zero derivative, rather than an extreme point like global or local minimum or transition state. The lattice bendings along two perpendicular directions lead to formation of nanotubes with potential energy crossing at zero curvature. Application of von Neumann−Wigner theorem to large-diameter tubes proves that 2D sp2/sp3 nanostructures are correlated transition states between two symmetrically equivalent bent structures. The stability and characteristics of induced spin polarization of C60 and pentacene molecules as well as carbon nanotubes, graphene and h-BN zig-zag nanoribbons on several half-metallic and ferromagnetic surfaces were studied by electronic structure calculations. It was found that physisorption of the molecular and graphene zig-zag nanoribbon agents causes noticeable spin polarization of the carbon nanofragments, converting graphene nanoribbons to 1D half-metal, stabilized by half-metallic LSMO(001) support.

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