Theoretical Characterization Of X-ray Spectra Of Fullerene C₈₀ And Nano Onion-like Fullerene C₂₀@C₈₀

Fullerenes are an allotrope of elemental carbon.Since the discovery of fullerene,it has been widely concerned in the scientific field because of its excellent physical and chemical properties.At present,various methods have been developed for the preparation of fullerene which is a convex polyhedron composed of pentagons and hexagons,and related researches and practical applications of fullerenes have also developed rapidly.Many fullerenes and fullerene products have been obtained and characterized by experiments and have potential applications in the fields of materials science,electromagnetic and energy,etc.In 1992,Professor Ugart discovered a new carbon material,namely onion-like fullerene,by arc discharge method.The discovery of nano onion-like fullerene has drawn great attention from the scientific community.Nano onion-like fullerene?NOLFs?is a new member of the fullerene family after C₆₀and carbon nanotubes,which consists of hollow concentric graphite spheroids.Due to the special mechanical,optical,electromagnetic,adsorption and catalysis properties of NOLFs,it has wide range of applications in engineering,energy,national defense,electronic information and medicine,and so on.There are a lot of isomers in fullerene and NOLFs,and the identification of isomers of fullerenes family system is a fundamental problem in their research field.Among these carbon cluster molecules,the system structures which accord with the isolated pentagon rule?IPR?are relatively stable,so these configurations are easy to be purified and synthesized and consequently their great researcher and application value.Up to now,X-ray spectroscopy has always been one of the most widely used spectral techniques.X-ray spectroscopy can be used to qualitatively and quantitatively analyze elements by using the energy distribution of excitation and de-excitation of core orbital electrons in molecular system.The X-ray spectra used in this paper include X-ray photoelectron spectra?XPS?and near-edge X-ray absorption fine structure?NEXAFS?spectra.XPS can provide core orbitals information by ionization of core electrons,which can reflect the sensitivity on local environment of elements,and has a certain dependence on the configurations of different symmetries.NEXAFS spectroscopy can accurately provide the virtual orbitals information through excitation of core electrons to unoccupied orbitals,thereby effectively reflecting the electronic structure and chemical structure of the system,which has obvious dependence on different symmetry structures and different configurations.Therefore,XPS and NEXAFS can be effectively used to identify isomers of fullerene and onion-like fullerene.In this work,we used the density functional theory?DFT?combined with the full core hole?FCH?approximation to simulate the C1s XPS and NEXAFS spectra of seven fullerene C₈₀ isomers following IPR and the two stable NOLFs C₂₀@C₈₀ isomers.The main contents and conclusions of this paper are as follows:Fullerene C₈₀ has seven isomers that satisfy IPR.The XPS and NEXAFS spectra of these seven isomers at the carbon K-shell?1s?have been simulated theoretically.The XPS roughly shows its dependence on fullerene C₈₀,so that it can not be utilized to identified these seven isomers.However,the NEXAFS spectra exhibits strong structural dependence on the seven molecules,therefore the NEXAFS spectra can be used to distinguish effectively the seven fullerene C₈₀0 configurations.In addition,we also classify carbon atoms according to their chemical environments and study the spectra produced by these carbon types.We found that the spectrum depends not only the local environment around carbon atoms,but also on other reasons,just like curvature of fullerene.The theoretical characterization of the X-ray spectrum of fullerene C₈₀0 is favorable for further experimental study of C₈₀.Onion-like fullerene C₂₀@C₈₀0 possesses two stable isomers C₂₀@C₈₀(D_5d)and C₂₀@C₈₀(D_5d?).We calculated theoretically the C1s XPS and NEXAFS spectra of these two configurations by means of DFT method with with the FCH approximation.Both XPS and NEXAFS spectra display obvious dependence on NOLFs C₂₀@C₈₀0 structure.The two onion-like fullerene isomers can be easily identified by using spectral characteristic differences from our calculated X-ray spectra.We also calculated the spectra of carbon atoms in different local environments in order to explore the origins of spectral features and further understand the dependence of X-ray spectra on different structures.Moreover,we computed the X-ray spectra of NOLFs C₂₀@C₈₀ based on the building block?BB?principle,and compared BB results with data of our theoretical calculation.It is noted that the results of BB principle are inconsistent with the theoretical values.So the X-ray spectrum of onion-like fullerene C₂₀@C₈₀ could not be calculated using the BB method.We verify the applicability of the BB principle to quickly calculate the X-ray spectra of NOLFs C₂₀@C₈₀,which is helpful to analyze the chemical and electronic structure changes when the small fullerene C₂₀0 is embedded into the large fullerene C₈₀.There are six chapters in this paper.The first chapter is the preface,which mainly describes the background of the research on the X-ray spectrum at the carbon K-shell?C1s?of fullerene family system.The second chapter mainly introduces the basic quantum chemistry theory which is related to our research work.The third chapter mainly introduces the theory of X-ray spectrum.In chapter 4,we mainly describe the X-ray spectrum characterization of seven IPR isomers of fullerene C₈₀.The seven isomers can be distinguished by using the structural dependence of the XPS and NEXAFS spectra on fullerene C₈₀.In chapter 5,we mainly describe the X-ray spectrum characterization of two stable configurations of NOLFs C₂₀@C₈₀.We calculated theoretically the XPS and NEXAFS spectra of these two configurations.The two isomers can be effectively identified by the relationship between spectrum and structure.We also calculated the spectra of carbon atoms in different chemical environment so that we could understand the origins of the spectral features in depth.Additionally,we studied the feasibility of rapidly calculating the X-ray spectrum by the BB approach for onion-like fullerene system,and finally it is fully proved that the BB principle could not be used to calculate the XPS and NEXAFS spectra of onion-like fullerene C₂₀@C₈₀.The sixth chapter summarized the main work of this paper.