Extended Data Fig. 6: Structural evolution of C60 under room-temperature compression.
a, Structure model (Only one layer is shown) of C60 under 30 GPa and room temperature (300 K), obtained by classic and ab initio MD. Under high pressure (30 GPa), the inter-molecule distance reduces to 0.86 or 0.87 nm from 1.0 nm. During compression to 30 GPa at room temperature, the buckyballs are deformed and inter-buckyball bonding occurs by formation of four-fold (sp3) bonds (15%). In this and the following figures, the atoms with sp3 bonding are colored in blue. The fraction of sp3 atoms was approximated by the number of 4-fold coordinated atoms within a cut off distance (in this work, rcut = 1.85 Å). We shall point out that, the sp3 fraction calculated this way is slightly underestimated in comparison to that calculated quantum-mechanically, e.g., with the maximally localized Wannier function (MLWF). b, In situ Raman spectra of C60 under compression (up to ~32 GPa) without pressure transmitting medium, with an excitation wavelength of 532 nm. With increasing pressure, the Raman peaks of the Ag mode corresponding to the breathing of totally symmetric vibrations and the Hg mode are gradually broadened with decreased intensity, suggesting a gradual decline of the symmetric environment of pristine C60, associated with the polymerization of buckyballs69 and the formation of sp3 bonds70, consistent with our theoretical results.
