Theoretical study of nano onion-like fullerenes C₂₀@C₈₀ on XPS and NEXAFS spectra

The X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy of the carbon K-edge for the two nano onion-like fullerenes (NOLFs) C${}_{20}@C_{80}$ isomers have been in theory performed by density functional theory (DFT) method. We have especially focussed on the structure-spectroscopy relationship by exploring in detail and analyzing systematically the calculated spectra. Both the XPS and NEXAFS spectra show dependence on molecular structures, so these two spectroscopic techniques can be used to identify the two NOLFs C${}_{20}@C_{80}$ isomers. Meanwhile, the spectral components of each C${}_{20}@C_{80}$ isomer based on the local environment of carbon atoms have been calculated at the same level. Furthermore, we have tested the feasibility of using the building block (BB) approach to quickly estimate the XPS and NEXAFS spectra in the NOLFs C${}_{20}@C_{80}$ system. Results show that applying the BB approach is impossible to predict the direct calculated results for the NOLFs C${}_{20}@C_{80}$. Additionally, fullerene C${}_{100}$(D${}_2$) as an isomer of C${}_{20}@C_{80}$ can be distinguished from the two C${}_{20}@C_{80}$ isomers by the XPS and NEXAFS spectra.