Theoretical Study On The Stacking Interaction Between Small Molecules And Graphene

We have researched the property of the graphene and the interaction betweengraphene and small molecules using the density functional tight binding method withthe empirical London dispersion energy term (DFTB-D).The interactions between a benzene molecule and multilayer graphenes have beenstudied in this work using a density-functional tight-binding method. Analysis ofstructural characteristics, energetics, charge distribution etc., uncovers remarkablecharge transfer resulted from a strong interaction between the ionic benzene andneutral multilayer graphene that is not attained for their neutral counterparts, with aclear interesting trend of charge accumulation at the surface region. Moreover, theadsorption energy increases gradually as the increase of the number of graphenelayers and the electronic density of states of the multilayer graphene is simplyequivalent to the multiple of that of a single layer. The band gap of the multilayergraphene varies with the number of layers, which is not affected by the adsorption ofionic benzene but is altered by the neutral benzene adsorption by0.05eV.The strong charge transfer makes the electrification property of small benzenemolecule obviously stronger than that of cyclical graphene, and this fact indicates thatthe size of graphene will affect its electrical property. We further have studied thesize effects for aperiodic graphene using the SCC-DFTB method. In both cases withand without hydrogen, we have calculated the structure, energy, charge distribution,etc, in aperiodic graphene with the uniform expansion in size in the neutral and ionsystems, respectively. We found that the multiple effect is not obvious with the increasing uniform of grapheme size. Optimized structures showed that thedeformation of the structure had taken place in the neutral and ionic systems and theprocesses of deformation are in a similar way. The structure where the deformationdid not happen can remain the flat form in both systems. The deformation of thegraphene structure has an important influence on the ionization energy, band gap andorbital energy. We found that the differences of system and the existance of hydrogencould influence the ionization energy, charge distribution, band gap and orbitalenergy. Our current findings highlight the importance of the correlation between thesize and nature of graphene, and also provide a new insight into the mechanism ofcomplex nature of graphene at the atomic level.