First-Principles Investigation on Structural and Optical Properties of M+@C60 (Where M = H, Li, Na, and K)

Abstract

Structural and optical properties of proton and alkali-metal atom cation encapsulated inside C60 molecule, M+@C60 (where M = H, Li, Na, and K), are investigated in detail by first-principles. Two possible ground state atomic geometries where M+ can exist outside or inside C60 are proposed by the optimization using the B3LYP hybrid functional based on the density functional theory. From the potential energy surface obtained in the same level calculation, we confirm that the energy barrier existing at the surface of C60 plays an important role to confine M+ inside. We also apply an all-electron GW + Bethe–Salpeter method based on the many-body perturbation theory and calculate the (inverse) photoemission spectra and the photoabsorption spectra. The calculated spectra are in reasonable agreement with available experimental results, while minor deviation exists, suggesting a non-negligible environment effect.