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High-Level Multireference Investigations on the Electronic States in Single-Vacancy (SV) Graphene Defects Using a

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Graphene's single carbon vacancy (SV) defect induces nonplanar structures. Calculations reveal that these nonplanar configurations are more stable than planar ones, with significant energy stabilization observed in highly deformed structures.

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Area of Science:

  • Computational Chemistry
  • Materials Science
  • Condensed Matter Physics

Background:

  • Graphene, a single layer of carbon atoms, is a 2D material with unique electronic and mechanical properties.
  • Carbon vacancies (SV) are common defects in graphene that can significantly alter its properties.
  • Understanding the structural and electronic consequences of SV defects is crucial for graphene-based applications.

Purpose of the Study:

  • To investigate the nonplanar structural characteristics of graphene with a single carbon vacancy (SV) defect.
  • To determine the ground state and energetically close excited states of the SV defect in graphene.
  • To explore the stability and structural evolution of graphene with SV defects through theoretical calculations.

Main Methods:

  • Utilized a pyrene-SV model system to represent graphene with a single carbon vacancy.
  • Employed complete-active-space self-consistent field theory (CASSCF) for electronic structure calculations.
  • Applied multireference configuration interaction singles and doubles (MR-CISD) calculations to refine energy levels and excited states.

Main Results:

  • Optimized planar structures exhibit a 3B1 ground state, with three other states within 1 eV, but these are saddle points.
  • Following imaginary frequencies leads to more stable, nonplanar structures (Cs symmetry), with the 1A' state being lowest in energy and L-shaped.
  • Further deformation results in the most stable singlet structure (C1 symmetry), featuring a new bond that stabilizes the system by over 3 eV compared to the planar 3B1 state.

Conclusions:

  • Single carbon vacancies in graphene promote significant nonplanar deformations.
  • Nonplanar structures, particularly those with additional bonding, are substantially more stable than planar configurations.
  • The study provides insights into the defect-induced structural flexibility and stability of graphene.