Applicability of Density Functional Tight Binding Method with Dispersion Correction to Investigate the Adsorption of Porphyrin/Porphycene Metal Complexes on Graphene

Abstract

Applicability of self-consistent-charge density-functional tight-binding method with dispersion correction (SCC-DFTB-D) was tested to the graphene adsorption of medium-sized molecules. We computed adsorbed structures of transition-metal complexes of porphyrin and porphycene on graphene, and evaluated the adsorption energies. The energies reasonably corresponded to the reference values evaluated by density functional theory (DFT) calculations. Furthermore, we confirmed the model size dependence of energy less than 1 kcal mol ¹1 by expanding the graphene size. SCC-DFTB-D can be an alternative choice for the computation of graphene adsorption of large molecules that are out of scope for typical DFT in terms of the computational cost.Graphene is a well-known versatile material composed of sp 2 carbons, whose significant electron mobility, mechanical strength, and optical properties have been widely investigated for the development of the nanotechnology. 1 Graphene has also been developed as an advanced material for molecular storage and gas sensing.2,3 Various chemical species like H 2 , CO 2 , and H 2 O are known to adsorb on graphene surface, whose capacity can be facilitated by some minor modulations.While most of the previous studies focused on the adsorption of gaseous small molecules on graphene, adsorption of larger molecules recently came to be investigated, and the novel utilities of graphene emerged accordingly. The efficient adsorption of antibiotics was confirmed by liquid chromatographytandem mass spectrometry, suggesting its role as an antibiotics filter for industrial wastewater. 4 Another possible utility was suggested as a sample support for the imaging of proteins by electron microscopy and electron holography.57 Typical approach to obtain the biomolecular structures was crystallography with X-ray or neutron diffraction, which provides the averaged image of a protein crystal. The imaging on graphene surface can, in contrast, provide the picture of a single protein. Therefore, we can expect that the detailed structure of a single native protein is resolved on graphene.The computational studies of graphene adsorption have often been done with density functional theory (DFT), 8 to evaluate the adsorbed structures, the adsorption energies, and chemical reaction pathways on graphene. 4,9,10 It is, however, difficult to perform DFT calculation for larger-sized molecules due to computational costs. A candidate for an alternative method with lower computational cost would be the self-consistent-charge density-functional tightbinding method (SCC-DFTB), 11 which omits time-consuming integral calculations by empirical parametrization. It should be noted that the dispersion interaction, which is not taken into account in DFTB, can be the dominant contributor in the calculation of graphene adsorption. Therefore, dispersion correction is indispensable for adsorption calculation, although the dispersion-corrected SCC-DFTB (SCC-DFTB-D) has scarcely been utilized for large molecular clusters.In this study, we calcu...

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