A DFT Analysis for the Electronic Structure, Mulliken Charges Distribution and Frontier Molecular Orbitals of Monolayer Graphene Sheet

Abstract

As a density functional theory (DFT) offers a wide variety of calculations for computing structures and properties of multi-electron atomic or molecular systems, the two-dimensional (2D) periodic boundary condition (PBC) calculations of it is especially recommended for investigating ground state electronic structure of the graphene like materials. In this study, the 2D PBC calculations of DFT are performed on the 2D monolayer graphene sheet and produced its ground state electronic structure. The hexagonal, honeycomb-like pattern of the carbon rings are confirmed in its optimized geometry. The inhomogeneous partial atomic charges in its terminal and nonterminal carbon atoms are observed by the Mulliken population analysis method, which is in accordance with the experimental findings. The HOMO−LUMO energy gap calculated from their DFT computed eigenvalues is ΔE = 0.0018 eV, indicating a facile redistribution of electrons in them. Such unique characteristic of the monolayer graphene sheet has not only unlocked the superconducting tendency of the graphene-based materials but also speculated a high possibility of involving such frontier molecular orbitals (FMOs) in the chemical reactions that usually take place as a result of giving and/or taking electrons. The electron density surface of FMOs computed by the DFT model are mostly found to localize at terminal regions of the graphene sheet, particularly indicating such regions as chemically more active. It is believed that the theoretical findings presented here will be very useful while tuning graphene properties either by doping with metals/metalloids or by adding functional molecular parts in the graphene rings.