A First Principle Study Of Low Dimentional Carbon Materials And Their Stability

Low-dimensional carbon materials have various nanostructures, which could greatly influence the properties of the material. Therefore, we could modify the structure of a certain material in order to obtain the desired properties. Research on graphyne nanoribbons is just rising, and only a few research relevant to the properties of graphyne nanoribbons are reported. It is reported that zigzag a-graphyne nanoribbons (ZaGNR) exhibit half metallicity under a transverse electrical field, so ZaGNR could be used in the area of spintronics. The energy difference between the antiferromagnetic ground state and ferromagnetic metastable state is so small that the ground state can not exist stably at room temperature. However, the half metallicity relies on the antiferromagnetic ground state structures, so exploring new methods to help stabilize the ZaGNR’s ground state at room temperature is of practical significance. Research on metal endohedral fullerene has lasted a long time, but its contribution to find the smallest fullerene was not proposed until2012Professor Kroto’s group synthesized M@C28, which fulfilling the32electron rule. Therefore, a new method for exploring the smallest fullerene was proposed. So far, research on metal encapsuled in C20fullerene satisfying the32electron rule has not been reported in the literature. In this dissertation, factors influencing the stability of ZaGNR and metal encapsulated C20fullerene and related mechanism are studied.When exploring the stability of ZaGNR’s ground state, we first used Siesta software comparatively calculated the geometrical and electronical structures of monohydrogenated and dihydrogenated ZaGNR. It was found that the ground state of monohydrogenated and dihydrogenated ZaGNR are in antiferromagnetic state. When compared with monohydrogenated ZαGNR, the band structure changed significantly in the dihydrogenated case, namely, the edge state evolved from the previous (2π/3, π) to (0,2π/3), and in the antiferromagnetic state the direct band gap turned into an indirect band gap. In the monohydrogenated ZaGNR, wave function of edge state were strongly localized but delocalized in the dihydrogenated ZaGNR. By analyzing the energy of monohydrogenated and dihydrogenated ZaGNR, it was observed that the energy difference between antiferromagnetic ground state and ferromagnetic metastable state was greatly enlarged in dihydrgenated ZaGNR when compared with the monohydrogenated case. And the energy difference was large enough to make dihydrogenated ZaGNR existed in its ground state stably under the room temperature. At last, the influence factors of the stability of ZαGNR’s ground state was discussed, discovering the magnetic moments’s magnitude and direction of the four middle carbon atoms magnetic moment determined the stability of the system.When studying the geometrical structure and electronic properties of the C20fullerene and M@C20clusters (M=Eu3-, Am3-, Gd2-, Cm2-, Tb-, Bk-, Dy, Cf, Ho+, Es+, Er2+, Fm2+, Tm3+, Md3+, Yb4+, No4+, Lu5+and Lr5+), we first employed Gaussian09software to optimize the the structures with different functionals. It was observed that when encapsulated with an f-block atom/ion, the symmetry of C20fullerene would be turned from D2h to Ih, and the the frequency analysis confirmed that all the clusters were stable structures. By using binding energy and the HOMO-LUMO gap, we found that when encapsulated an f-block atom/ion in C20fullerene, the stability increased a lot when compared with bare C20fullerene. Finally, after analyses of population, electron localization function, orbital component and QTAIM, we found that strong hybridization between s, p, d and f orbitals of metal atom/ion and2p orbital of carbon atom as well as the covalent bond between metal atom/ion and carbon atom lead to the increase in the stability of the system.