First Principles Investigations Of The Transport Properties Of XC₆H₄X Molecular

Density Functional Theory (DFT) is an effective method of studying the electron structure of many-electron system. With this theory, the properties of a many-electron system can be determined by using functionals, which in this case is spatially dependent on electron density. Since the 1990's, when the exchange and correlation interactions were used in the approximation, the results of DFT calculations for solid-state systems agreed more satisfactorily with experimental data. DFT is now a successful method for electronic structure calculations in chemistry and solid-state physics. With the rapid development of computer hardware and software, a variety of DFT calculation software has been developed, such as ATK, ADF etc. Clusters, because of the size, which is between atomic and macro system, with its own diversity and singular nature, become the important research object.We have performed first-principles calculations on the reconstructed molecule of benzene. We made up a new molecule of XC₆H₄X by replacing two symmetrical H atoms in the benzene molecule by S, Se and Te. We have built the simulation of XC₆H₄X by ATK and VNL, and we have optimized the structure of XC₆H₄X. Then we have built two Co(001) electrodes beside the XC₆H₄X, which constructed a kind of two probe system. Finally, we have studied the DOS and transmission spectrum of the two probe system. Our work is concluded in three aspects.We have optimized the structures of XC₆H₄X by the mathematical method of quasi-Newton. The result of calculation shows that the structures of XC₆H₄X are different from the original structure of benzene. We have calculated total energy of XC₆H₄X and our interest is the lowest energy which is most stable.We have considered different adsorption sites for the X atom linked to the Co (001) electrode. Three modes have been considered, the hollow site, the bridge site and the top site. We have found that the hollow site is most stable. Further more, we have compared the result of LDA and GGA. We have also studied the situation of spin polarized electrode ion at the hollow site, and the discovery is that the spin polarization causes the increasing distance of X atom to Co(001) electrode.Finally,we have calculated the DOS and transmission spectrum of the non-spin polarized two probe system Co-XC₆H₄X-Co. The DOS shows that Co-SC₆H₄S-Co, Co-SeC₆H₄Se-Co and Co-TeC₆H₄Te-Co has minor changes. The results show that the different atom has different bonding orbital energy. Studying from the transmission coefficient, we have found that there exist resonance tunneling in the two probe system and the resonance tunneling capability of Co-SC₆H₄S-Co is more than Co-SeC₆H₄Se-Co and Co-TeC₆H₄Te-Co.