The Different Story of π Bonds

Cappelletti, Marco; Leccese, Mirko; Cococcioni, Matteo; Proserpio, Davide M.; Martinazzo, Rocco

doi:10.3390/molecules26133805

Cited by 2 publications

(2 citation statements)

References 60 publications

(94 reference statements)

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“…Unlike carbon, the arrangement of silicon and germanium atoms in a honeycomb lattice is unstable in a planar geometry and is subject to a structural distortion that consists of a relative out-of-plane displacement of the two sublattices by 0.53 and 0.63 Å, respectively. 60,61 Despite the marked difference in the crystal structure, the fieldinduced semiconductor-to-semimetal transition is preserved, as evident from Figure 4e,f. The energy gap closes at weaker critical fields than in the case of graphene nanoribbons.…”

Section: T H Imentioning

confidence: 92%

“…To further illustrate that this field-induced transition to the Dirac semimetal is of a general nature, we investigate heavier group-IV congeners of graphene nanoribbons, that is, silicene and germanene nanoribbons. , Such nanostructures have been epitaxially grown on various substrates, − including inert substrates, − that are instrumental to preserving the ideal honeycomb configuration, and subsequently integrated as active channels into electronic devices. , Figure d displays the atomic structure of hydrogen-terminated silicene and germanene nanoribbons. Unlike carbon, the arrangement of silicon and germanium atoms in a honeycomb lattice is unstable in a planar geometry and is subject to a structural distortion that consists of a relative out-of-plane displacement of the two sublattices by 0.53 and 0.63 Å, respectively. , Despite the marked difference in the crystal structure, the field-induced semiconductor-to-semimetal transition is preserved, as evident from Figure e,f. The energy gap closes at weaker critical fields than in the case of graphene nanoribbons.…”

Section: Electric Route To Dirac Fermions In Agnrsmentioning

confidence: 98%

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Electrically Induced Dirac Fermions in Graphene Nanoribbons

et al. 2021

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Graphene nanoribbons are widely regarded as promising building blocks for next-generation carbon-based devices. A critical issue to their prospective applications is whether their electronic structure can be externally controlled. Here, we combine simple model Hamiltonians with extensive first-principles calculations to investigate the response of armchair graphene nanoribbons to transverse electric fields. Such fields can be achieved either upon laterally gating the nanoribbon or incorporating ambipolar chemical codopants along the edges. We reveal that the field induces a semiconductor-to-semimetal transition with the semimetallic phase featuring zero-energy Dirac fermions that propagate along the armchair edges. The transition occurs at critical fields that scale inversely with the width of the nanoribbons. These findings are universal to group-IV honeycomb lattices, including silicene and germanene nanoribbons, irrespective of the type of edge termination. Overall, our results create new opportunities to electrically engineer Dirac semimetallic phases in otherwise semiconducting graphene-like nanoribbons.

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Section: T H Imentioning

confidence: 92%

Section: Electric Route To Dirac Fermions In Agnrsmentioning

confidence: 98%

Electrically Induced Dirac Fermions in Graphene Nanoribbons

et al. 2021

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On the nature of the chemical bond in valence bond theory

Shaik

Hiberty

2022

The Journal of Chemical Physics

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This perspective outlines a panoramic description of the nature of the chemical bond according to valence bond theory. It describes single bonds, and charge-shift bonds (CSBs) in which the entire/most of the bond energy arises from the resonance between the covalent and ionic structures of the bond. Many CSBs are homonuclear bonds. Hypervalent molecules are CSBs. Then we describe multiply bonded molecules with emphasis on C2 and 3O2. The perspective outlines an effective methodology of peeling the electronic structure to the necessary minimum: a structure with a quadruple bond, and two minor structures with double bonds, which stabilize the quadruple bond by resonance. 3O2 is chosen because it is a persistent diradical. The persistence of 3O2 is due to the large CSB resonance interaction of the π-3-electron bonds. Subsequently, we describe the roles of π vs. σ in the geometric preferences in unsaturated molecules, and their Si-based analogs. Then, the perspective discusses bonding in clusters of univalent metal-atoms, which possess only parallel spins, and are nevertheless bonded due to multiple resonance interactions. The bond energy reaches ~40 kcal/mol for a pair of atoms (in n+1Cun; n~10-12). The final subsection discusses singlet excited states in ethene, ozone and SO2. It demonstrates the capability of the breathing-orbital VB method to yield an accurate description of a variety of excited states using 10 or less VB structures. Furthermore, the method underscores covalent structures which play a key role in the correct description and bonding of these excited states.

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The Different Story of π Bonds

Cited by 2 publications

References 60 publications

Electrically Induced Dirac Fermions in Graphene Nanoribbons

Electrically Induced Dirac Fermions in Graphene Nanoribbons

On the nature of the chemical bond in valence bond theory

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