Electronic structure of 1,4-Phenylenediacrylic acid on graphene and bilayer graphite: from experiments to DFT and ab initio molecular dynamics simulations

Abstract

In this work, density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations were implemented to expand the knowledge about the interaction of graphene and bilayer graphite surface with 1,4-Phenylenediacrylic acid (C₁₂H₁₀O₄). The DFT calculations demonstrated that C₁₂H₁₀O₄ molecule has an opening band gap of 0.0062 eV at the top position over the graphene sheet higher than the cross and bridge sites with lower band gaps of 0.0050 eV and 0.0046 eV, respectively. The HOMO-LUMO splitting calculations confirmed more mixture of LUMO states of the C₁₂H₁₀O₄ and graphene in the carbon-carbon double bond in vinyl segment and the COOH functional group in the C₁₂H₁₀O₄@Graphene (top) adsorption site. Then, the increasing of the molecule units on the graphene substrate resulted in a higher electronic band gap of 0.0068 eV and LUMO energy level of 0.9528 than 0.9383 eV for the monomer ones. The AIMD calculations were used to mimic the self-assembly process of the C₁₂H₁₀O₄ molecules on the graphene layer at room temperature, remarking high adsorption capabilities of the latter one. The imaginary and real parts of dielectric constant have been evaluated and for all cases the maximum intensity of the main first peak has been found at 2.43 THz. The results of the static part of dielectric constant showed high Re(ω) for the adsorption of C₁₂H₁₀O₄ monomers on the graphene surface, while by increasing the number of C₁₂H₁₀O₄ units Re(ω) resulted remarkably reduced. The maximum value predicted is 7817 in C₁₂H₁₀O₄@Graphene (cross) along the in-plane xx polarization and 2747 for 4C₁₂H₁₀O₄@Graphene along the in-plane yy directions. Finally, the adsorption of C₁₂H₁₀O₄ layer on the AB stacking bilayer graphite has been considered to simulate the experimental scanning tunnelling microscopy (STM) image of self-assembled C₁₂H₁₀O₄ on highly oriented pyrolytic graphite (HOPG) surface. The zero-band gap has been predicted since the electronic structure of graphene near the K point varies by increasing its thickness.