Font Size: a A A

The First Principles Study On Several New Carbon-Based Nano Functional-Materials

Posted on:2011-12-10Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z X ZhangFull Text:PDF
GTID:1101360305971342Subject:Materials science
Abstract/Summary:PDF Full Text Request
The characteristics of new-carbon materials cover all the natures of substances, even the opposite ones from the hard to very soft, all absorption and all transmission, insulator - semiconductor - high conductor, insulation - good thermal conductivity, high ferromagnet, high critical temperature superconductors, etc. Owing to their novelty in optical,electronic,magnetic,thermal,or mechanic properties, carbon nanomaterials have attracted intensive research interest.Because of the independence of empirical parameters, the first principle study has become the main research means in condensed matter physics, quantum chemistry and materials science. In this paper, some novel materials with different dimensions,such as fullerene,nanotube,and graphene,were studied on the basis of the first principles calculations.The results are summarized as follows:(1) The geometric and electronic structures of fullerenes encapsulating trimetallic nitride cluster Tb3N@C84 were studied using the density functional theory. Geometric optimization showed that Tb3N@C84 that violates the Isolated-Pentagon Rule (IPR) with a pentalene unit formed by fused pentagon pair is the most kinetically stable isomer with the largest energy gap. Compared to IPR-violating Tb3N@C84 isomers, IPR-Tb3N@C84 is the most thermodynamically favorable endohedral compound with the lowest energy. The interaction between Tb3N and C84 is ionic and Tb3N@C84 has a higher density of states (DOS) than empty C84 molecule at the Fermi energy, indicating that the embedment of Tb3N unit can increase the conductance of C84.(2) The electronic parameters of fullerenes are essential for their potential use as active layers in organic solar cells. Two isomeric forms of [60] PCBM (phenyl-C61-butyric acid methyl ester) clusters were calculated using the B3LYP method with 6-31G(d) basis set. It has been found that the contraction of C6-6 double bonds is favorable for addition. The first Adiabatic Electron Affinity (AEA) for [60] PCBM is similar to that for C60. The energy gaps between the highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO) of [60] PCBM are reduced compared with C60. PCBM derivatives show increased level of LUMO of fullerenes. From the natural charge populations, it was found that adding PCBM unit onto the C60 cages does not change the charge populations remarkably; attaching a PCBM has no effects on the electronic structures of C60. The results of theoretical calculation suppose that PCBM is not involved in the process of photoelectric conversion, but plays a key role in adjusting the level of HOMO-LUMO for increasing photoelectric conversion efficiencies. Similar results were also reached for [70]PCBM.(3) The first principles study was performed on the stability of Ag adsorbed on the internal walls of single-walled carbon nanotube (SWCNT) and loaded on acid modified SWCNT. The calculation results show that Ag can be adsorbed stably on the internal walls of SWCNT. The adsorption energy increases as the diameter in a certain range. Ag can also be loaded on the modified SWCNT surface in the form of–COOAg and-OAg groups, and -COOAg group is more stable than -OAg group. For either tne adsorption on the inner SWCNT or the load on the modified SWCNT surface, only a small part of the Ag ions can be stably bonded to the wall of SWCNT. In other word, most of Ag ions observed in experiments are loaded or adsorbed on CNT by physical adsorption.(4) The adsorption of cysteine molecule on intrinsic and Au-doped or decorated graphene sheets was studied by density functional theory calculations. Compared with the intrinsic graphene, Au-doped or decorated graphene strongly adsorbs cysteine molecules with high binding energy value and short distance between the cysteine molecules and the graphene surface. The calculation of electron transfers and dipole moment supports the notion that Au doping or decorating influences the electronic properties of graphene substantially. Furthermore, the density of states results show the orbital hybridization between cysteine and Au-doped or decorated graphene sheet. Therefore, the calculations suggest that Au-doped or decorated graphene is a promising candidate for sensor detecting a variety of S-containing proteins and metalloenzymes. Pt-doped graphene sheets are also studied and the same conclusion was obtained.
Keywords/Search Tags:the isolated pentagon rule (IPR), endohedral metallofullerenes, carbon nano-tubes (CNTs), graphene, the first principles
PDF Full Text Request
Related items