3 years ago

Polygonal current models for polycyclic aromatic hydrocarbons and graphene sheets of various shapes

Polygonal current models for polycyclic aromatic hydrocarbons and graphene sheets of various shapes
Paolo Lazzeretti, Stefano Pelloni
Assuming that graphene is an “infinite alternant” polycyclic aromatic hydrocarbon resulting from tessellation of a surface by only six-membered carbon rings, planar fragments of various size and shape (hexagon, triangle, rectangle, and rhombus) have been considered to investigate their response to a magnetic field applied perpendicularly. Allowing for simple polygonal current models, the diatropicity of a series of polycyclic textures has been reliably determined by comparing quantitative indicators, the π-electron contribution to IB, the magnetic field-induced current susceptibility of the peripheral circuit, to ξ∥ and to σ∥(CM)=−NICS∥(CM), respectively the out-of-plane components of the magnetizability tensor and of the magnetic shielding tensor at the center of mass. Extended numerical tests and the analysis based on the polygonal model demonstrate that (i) ξ∥ and σ∥(CM) yield inadequate and sometimes erroneous measures of diatropicity, as they are heavily flawed by spurious geometrical factors, (ii) IB values computed by simple polygonal models are valid quantitative indicators of aromaticity on the magnetic criterion, preferable to others presently available, whenever current susceptibility cannot be calculated ab initio as a flux integral, (iii) the hexagonal shape is the most effective to maximize the strength of π-electron currents over the molecular perimeter, (iv) the edge current strength of triangular and rhombic graphene fragments is usually much smaller than that of hexagonal ones, (v) doping by boron and nitrogen nuclei can regulate and even inhibit peripheral ring currents, (vi) only for very large rectangular fragments can substantial current strengths be expected. © 2017 Wiley Periodicals, Inc. Circuits of π-electron current density JB in graphene fragments of various shapes. The strength of the electronic current density induced by a magnetic field at right angles to the molecular plane of polycyclic aromatic hydrocarbons and graphene sheets depends on their shape and size. Hexagonal (rhombic) fragments are characterized by stronger (weaker) strength measured via a current susceptibility index developed via a polygonal current model.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/jcc.25076

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