Controversy about electron structure of defects in graphene resolved

Scientists have resolved a long-standing controversy about electron structure of defects in wonder material graphene through a solution that is identical for all models used for calculation of the overall electronic structure of defects.

The international community of researchers have long been debating about electron structure of defects in graphene. Researchers describe the configuration based on a different number of variables and the model used. Researchers at the University of São Paulo’s Physics Institute (IF-USP), Brazil, came up with a solution that can be applied universally to all models and is compatible with experimental findings.

Scientists explain that there have been divergences in the community regarding whether the vacancy formed by removing a single carbon atom from a graphene sheet’s crystal lattice causes a weak or strong magnetic moment, and regarding the strength of the magnetic interaction between vacancies.

This particular vacancy prompts the surrounding atoms to rearrange themselves into new combinations to accommodate the absence of an atom, forming electron clusters known as “floating orbitals” at the vacant site.

Three important variables are associated with the phenomenon: electron density, i.e., how the electrons are distributed; electron levels, i.e., the energy levels occupied by the electrons; and magnetic moment, i.e., the torque produced in the electrons by an external magnetic field.

The study notes there are two ways to calculate the overall electron structure of the vacancy region, both derived from quantum mechanics: the Hartree-Fock (HF) method, and density functional theory (DFT). In DFT the calculation is performed by making each electron interact with average electron density, which includes the electron in question. In HF the operator used excludes the electron and considers only its interaction with the others. HF produces more precise results for electron structure but the calculation is far more laborious.

Scientists often combine the two methods by means of hybrid functionals, but they had never been used in the case of graphene. Scientists discovered the hybrid functional that best describes the material. When applied to several models using computer simulation, the new hybrid functional produced the same result for them all and this result matched the experimental data.

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