Theoretical Calculations On Electronic And Spectroscopic Properties Of Large Size Fullerenes

Physical and chemical properties of fullerenes relate to the number of carbon atoms.With the increase of carbon atoms,the nonlinear optical and superconducting properties of the fullerenes may be significantly enhanced,and larger carbon cages can accommodate more embedded metals and molecules to increase their application in medicine and catalysis.It is difficult to isolate fullerene isomers only with experimental means.Hence,in this work,a set of multi-scale calculation means was used to screen out stable IPR and non-IPR isomers of large size fullerenes,the electronic structure,electronic spectra of which were predicted to provide fingerprint information of the isomers.ZNIDO/SOS program was improved to calculate third order nonlinear optical(NLO)response of the isomers with external electric field.The research contents are as follows:D3d(3)@C96 and heterofullerene C72B12N12 and C71B12N12 Ti were investigated using density functional theory(DFT).The calculations showed that doping of BN pairs and Ti polarizes the electronic structure of those heterofullerenes,narrows their HOMOLUMO energy gaps,and leads to more electronic excitations in the UV/Vis region.Those heterofullerenes have strong NLO response at low external fields in the UV/Vis and infrared regions.With respect to the other five stable isomers(C2:181,D2:183,C1:144,C1:145,and C2:176),their HOMO-LUMO gaps are small and low-energy excitations are up to 500 nm.The stability of C2:181,D2:183,C1:144,and C1:145 is high and thermodynamic equilibrium dramatically affects the maximum responses of average NLO.DFTB and DFT were utilized to investigate the structures,electronic spectra,and third-order NLO response for the isomers of C106 and C112.For C106,only IPR isomers were taken into account.A possible correlation between the amount of connected pentagons(CPs,pentagons connected with a CC bond)and HOMO–LUMO gap was observed,as the conjugation of ? electrons of pentagons(through delocalization)stabilizes ? orbitals on pentagons,i.e.lowers the molecular orbital energies.UV/Vis spectra and IR were analyzed for the lowest energy isomers,in which some distinct fingerprints in UV/Vis and IR were analyzed to identify the isomers.The third order NLO properties of the lowest-lying six isomers of C106 were predicted with the ZINDO/SOS model under external fields up to 3.0 e V to check the response behavior of those isomers.With respect to C112,only non-IPR isomers with one or two APPs were considered.Therefore,3352 IPR isomers and 129073 non-IPR isomers satisfying APP?2 for C112 were taken for DFTB optimization.The characteristic IR fingerprint vibrations and absorption spectra of stable La2@C112 isomers have been assigned and these spectra help to identify isolated isomers in experiment.Geometry optimizations have been performed on icosahedral(Ih)fullerenes(C180,C240,C540,C720,and C960)by first principle calculations,in which the relationship of stability of fullerenes with C-C bond,POAV1 angle,radius of cage,spherical degree were discussed in detail.Only faceted Ih isomer exists for C180 and C240.The pentagon regions are chemical active center.The inter-particle interaction in the condense phase of these particles is of mainly electrostatic because of the uneven charge distribution on the particle surface.Red shift is observed in the IR and Raman spectra of these Ih fullerene particles.