Theoretical studies on electronic properties of curved graphene quantum dots and lithium adsorption on graphene quantum dots

Abstract

Graphene quantum dots (GQDs), with their attractive properties, are of interest to apply for electronic devices. Therefore, this dissertation aimed to investigate the electronic of curved graphene quantum dots (CGQDs) and the adsorption of lithium on GQDs. For the first part, two shapes of flat GQDs, rhomboidal (RGQDs) and hexagonal (HGQDs), were modified to make CGQDs with different folding axes and angles. Stabilities and electronic properties of CGQDs were studied using PBE/DNP. The results showed that the deformation energies of GQDs depend on sizes and folding axes but not their shapes. HOMO-LUMO gap variations, both widening and narrowing the gap, upon folding were observed, and can be explained by orbital interactions. In the second study, three sizes of GQDs, coronene, circumcoronene, and circumcircumcoronene were allowed to be adsorbed by lithium ions and atoms at various positions of GQDs. Adsorption positions and binding energies were determined using M06-2X/6-31g(d). The results indicated that lithium ion and atom could bind better at the edge of GQDs. The adsorption between lithium ion and coronene showed the highest binding affinity of -135.073 kcal/mol. Moreover, the size increment of GQDs raises the binding energy, except Li+ absorption on GQDs with -1 charge. Preferred adsorption positions of lithium ions and atoms on GQDs can be described by the total charge of six-membered ring. In addition, binding affinities of one-Li-ion system on GQDs are larger than two-Li-ion system. For two Li-ion system, the binding energy on GQDs also depends on Li ion-Li ion repulsion.