The doorsill of fullerene

► We explore how difficult it is for a guest atom to cut through C60 fullerene. ► The quasistatic processes of an atom going into and out from C60 along 3-fold axis. ► We explore geometrical, electronic structures, and energy changes in the processes. ► Stepping into C60 along 3-fold axis, an atom must span two thresholds. ► The higher threshold is located inside the C60 but not the outside.