DFT Study of the Structural Properties of Various Stacked Bilayer Graphdiyne and HCN Adsorption

HCN, as one of the cyanide species, is an extremely powerful and colorless poison. It is usually produced on an industrial scale and is a highly valuable precursor to many chemical compounds. Exposure of organism to HCN is highly toxic because it inhibits the consumption of oxygen by body cells[1]. Graphdiyne is a recently-synthesized carbon allotrope with a framework of sp and sp2 hybridized carbon atoms with high degrees of π-conjugation that features uniformly distributed pores. The hypothetical architecture was first designed by inserting four sp-hybridized carbon atoms into the sp2-sp2 bonds of graphene forming linear -C≡C-C≡C- linkages[2, 3] . In this work, all computations were performed using the spin polarized first-principle method as implemented in the Dmol3 code. The generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerh of (PBE) exchange-correlation functional was used, in combination with the double numerical plus polarization (DNP). The empirically-corrected density functional theory (DFT+D) method within in Grimme scheme was employed in all the calculation to consider the Van der Waals forces [4]. We used a 7×7×1 Gamma-centered Monkhorst–Pack k-grid for integration of Brillouin-zone and cut off 4.7 Å. We optimized four bilayer stacked configurations that nominated as AA, AB, AC, and AD. Results show that distance between layers is 3.482, 3.271, 3.126, and 3.168 Å, respectively. Also, the most stable bilayer configuration is the AC stacking and then AA, AB and AD stacking, respectively. In the following, we checked out the interaction tendency of AC stacking graphdiyne with HCN gas and its adsorption on the pristine bilayer graphdiyne was considered. In this regard, adsorption energy and band gap for all interacting systems are evaluated. Various directions for HCN namely perpendicular from N-head and H-head as well as horizontal direction were selected for approaching to graphdiyne plane. Also, center of 18-membered and hexagonal rings and top of acetylenic linkage were examined. The results showed that for center of 18-membered and hexagonal rings, horizontal direction is the best and has more adsorption energy than others and for acetylenic linkage perpendicular direction from H-head is the most stable configuration. After HCN adsorption, the band gap values and layer distances increased for all configurations.