Quantum Chemical Investigations on Functional Materials

This chapter provides a brief introduction to the different types of two-dimensional (2D) Dirac materials. The origin and the promising prospects of the Dirac point in the novel graphene-like 2D materials (graphynes) are well-deliberated. For example, α-, β- and γ-graphyne are well-established one-atom-thick two-dimensional (2D) materials in the graphyne family. These graphynes are mainly designed by incorporating an acetylenic linker (−C≡C−) at the CC double bond of graphene in different ratios. In the present chapter, we have modeled the novel analogs of α-, β- and γ-graphynes by increasing the number of acetylenic linkers and by expanding the sp2 network. Using this strategy, seven novel forms of 2D carbon frameworks (named as α2-graphyne, β4-graphyne, β5-graphyne, β6-graphyne, B-graphyne, circumcoro-graphyne (CCG), and coro-graphene (CG)) were designed. Further, the structure, stability, and electronic properties of novel forms of graphyne architectures were examined by using the computational methods within the framework of density functional theory (DFT). Phonon band dispersion analysis and molecular dynamics simulations authenticate the dynamic and thermal stability of all these 2D materials. Electronic structure calculations show that, four (α2-graphyne, β4-graphyne, B-graphyne, and CCG) 2D materials are semimetallic while the other three (β5-, β6-graphynes, and CG) are semiconducting in nature. The semimetallic sheets are furnished with multiple Dirac points, massless Dirac fermions and high Fermi velocities (0.24–0.99×106m/s). Anisotropic Dirac cones are observed in the case of CCG and B-graphyne.