Writing with ring currents: selectively hydrogenated polycyclic aromatics as finite models of graphene and graphane

Abstract

Alternating partial hydrogenation of the interior region of a polycyclic aromatic hydrocarbon gives a finite model system representing systems on the pathway from graphene to the graphane modification of the graphene sheet. Calculations at the DFT and coupled Hartree–Fock levels confirm that sp 2 cycles of bare carbon centres isolated by selective hydrogenation retain the essentially planar geometry and electron delocalization of the annulene that they mimic. Delocalization is diagnosed by the presence of ring currents, as detected by ipsocentric calculation and visualization of the current density induced in the π system by a perpendicular external magnetic field. These induced ‘ring’ currents have essentially the same sense, strength and orbital origin as in the free hydrocarbon. Subjected to the important experimental proviso of the need for atomic-scale control of hydrogenation, this finding predicts the possibility of writing single, multiple and concentric diatropic and/or paratropic ring currents on the graphene/graphane sheet. The implication is that pathways for free flow of ballistic current can be modelled in the same way.

Influence of Carbon Support on Electronic Structure and Catalytic Activity of Pt Catalysts: Binding to the CO Molecule

“…In the mixed X/Y basis set, the X basis is used for the C, O and H atoms and the Y basis is used for the Pt atoms. The ovalene molecule has been successfully used as a graphene model in previous studies [52][53][54] and here it only used for the basis set study and the C 54 H 18 molecule has been used in the rest of our calculation. As shown in Figure 1, the CO adsorption energy is converged to nearly the same value for the mixed TZ2P/QZ4P and QZ4P basis sets.…”

Assessment of the Performance of Optimally Tuned Range‐Separated Hybrid Functionals for Nuclear Magnetic Shielding Calculations

“…67 The existence of induced local currents [68][69][70] explains the shielding constants in aromatic and unsaturated compounds. 71,72 Current and spin density functional theory (CSDFT) [73][74][75][76][77][78] in principle takes into account the dependence of the xc functional on the current density. A few such schemes [79][80][81] exist but they are not widely available and are limited by suitable xc expressions.…”

The pseudo-π model of the induced magnetic field: fast and accurate visualization of shielding and deshielding cones in planar conjugated hydrocarbons and spherical fullerenes

“…This picture accounts well for the observed diatropic currents at the peripheral rings and paratropic currents at the central ring for coronene, as discussed in the literature. 53 Hence, the notable resemblance of B ind sz to B ind pz stems from the practically identical CMO contributions between conjugated hydrocarbons and the HSMs. The s MOs of the HSMs obey the same symmetry rules that determine the response of p MOs and consequently the pseudo-p model is suitable for the analysis of the magnetic response in terms of CMO contributions, as shown here.…”