First Principles Investigations Of The Electronic Transport Properties Of C₂₀ And Its Derivatives

The researches of molecular nano-device have become a hotspot, and aroused great interest among many experimentalists or theorists. In this thesis, we have performed calculations on the geometric,electronic structure,and electronic transport properties of C₂₀ fullerene and its derivates, based on first-principle density functional theory combined with nonequilibrium Green’s function.First, we investigate the geometric structure and electronic transport properties of the smallest carbon fullerene C₂₀ and its endohedrally doped M@C₂₀ （X=Li, Na, K） metallofullerenes. We firstly optimize the molecular structures by DMol3 package, and verify the stability by frequency analysis. Then we analyze the structural parameters, binding energies, and energy gaps of the optimized stable structures. The electronic transport properties are calculated by ATK software. It is found that the I-V curve of C₂₀ fullerene displays linear and nonlinear characteristics. Doping the alkali metal atom into C₂₀ cage makes its energy gap smaller, chemical activity more active, conductance increasing, and make the I-V curve display the negative differential resistance （NDR） behavior. These findings suggest that these metallofullerenes would have the potential value in molecular devices. We have explained them by analyzing the transmission spectrum, Molecular Projected Self-consistent Hamiltonian （MPSH）, and so on.Then we investigate the geometric structure and electronic transport properties of C₂₀H₂₀ and Li@C₂₀H₂₀ molecules to get to know the effect of environment. We obtain the stable structures of the two molecules, and calculate the transmission spectrum under zero and finite bias voltage. We also plot the I-V curves of the two molecules and obtain the conductances. The results display that the conductances of C₂₀H₂₀ and Li@C₂₀H₂₀ molecules are very small, which imply that the outer H atom is not beneficial to the charge transport of the two molecules. Doping the Li atom into C₂₀H₂₀ cage improves its conductance. Both the molecules display the nonlinear characteristics and NDR behavior under high bias voltage. These findings are meaningful to choose or design one molecular device.Last, we investigate the geometric structure and electronic transport properties of C₂₀F₂₀ molecule. We investigate the structural and electronic properties of C₂₀F₂₀ molecule, and calculate the transmission spectrum and conductance. We also plot the I-V curve of the molecule. It is found that C₂₀F₂₀ molecule has better chemical stability and charge transport capability. The I-V curve of C₂₀F₂₀ molecule displays better linear characteristic, which implies that it has stable conductance and would become one stable resistance device. These characteristics suggest that this molecule can be one important candidate of the molecular devices.