Accurate prediction of the electronic properties of low-dimensional XXXX derivatives using a screened hybrid density functional.

@entity505 @entity15583
Over the last several years, low-dimensional @entity15583 derivatives, such as @entity505 nanotubes and @entity15583 nanoribbons, have played a central role in the pursuit of a plausible @entity505 -based nanotechnology. Their electronic properties can be either metallic or semiconducting depending purely on morphology, but predicting their electronic behavior has proven challenging. The combination of experimental efforts with modeling of these nanometer-scale structures has been instrumental in gaining insight into their physical and chemical properties and the processes involved at these scales. Particularly, approximations based on density functional theory have emerged as a successful computational tool for predicting the electronic structure of these materials. In this Account, we review our efforts in modeling graphitic nanostructures from first principles with hybrid density functionals, namely the Heyd-Scuseria-Ernzerhof (HSE) screened exchange hybrid and the hybrid meta-generalized functional of Tao, Perdew, Staroverov, and Scuseria (TPSSh). These functionals provide a powerful tool for quantitatively studying structure-property relations and the effects of external perturbations such as chemical substitutions, electric and magnetic fields, and mechanical deformations on the electronic and magnetic properties of these low-dimensional @entity505 materials. We show how HSE and TPSSh successfully predict the electronic properties of these materials, providing a good description of their band structure and density of states, their work function, and their magnetic ordering in the cases in which magnetism arises. Moreover, these approximations are capable of successfully predicting optical transitions (first and higher order) in both metallic and semiconducting single-walled @entity505 nanotubes of various chiralities and diameters with impressive accuracy. This versatility includes the correct prediction of the trigonal warping splitting in metallic nanotubes. The results predicted by HSE and TPSSh provide excellent agreement with existing photoluminescence and Rayleigh scattering spectroscopy experiments and Green's function-based methods for @entity505 nanotubes. This same methodology was utilized to predict the properties of other @entity505 nanomaterials, such as @entity15583 nanoribbons. @entity15583 nanoribbons may be viewed as unrolled (and passivated) @entity505 nanotubes. However, the emergence of edges has a crucial impact on the electronic properties of @entity15583 nanoribbons. Our calculations have shown that armchair nanoribbons are predicted to be nonmagnetic semiconductors with a band gap that oscillates with their width. In contrast, zigzag @entity15583 nanoribbons are semiconducting with an electronic ground state that exhibits spin polarization localized at the edges of the @entity505 nanoribbon. The spatial symmetry of these magnetic states in @entity15583 nanoribbons can give rise to a half-metallic behavior when a transverse external electric field is applied. Our work shows that these properties are enhanced upon different types of oxidation of the edges. We also discuss the properties of rectangular @entity15583 flakes, which present spin polarization localized at the zigzag edges.
