We use Monte Carlo simulations to investigate properties of systems of ${\mathrm{C}}_{60}$ molecules inside (10,10) and (15,15) nanotubes. In the case of the (10,10) nanotube, ${\mathrm{C}}_{60}$ molecules form a quasi-one-dimensional system. The thermodynamical properties of this system such as energy and heat capacity are found to be very close to the properties of a one-dimensional system to which interaction with a nanotube is added. The structural properties are found to be insensitive to the quasi-one-dimensional nature of the system and are the same as those calculated for a one-dimensional system of ${\mathrm{C}}_{60}$ molecules. The transformation from a periodic to a nonperiodic state (“melting”) is a gradual one and cannot be detected through the heat capacity. Inside the (15,15) nanotube, a system of ${\mathrm{C}}_{60}$ molecules behaves differently. Most notably, the heat-capacity curve shows an extra peak when compared to the result for the (10,10) case. We show that this is due to the “melting,” i.e., transformation of a zigzag structure existing at low temperatures to a disordered one. We also show that systems with very high density $\mathrm{}(>95\%)\mathrm{}$ do not show this peak and “melt” differently.

• Received 13 February 2003

DOI:https://doi.org/10.1103/PhysRevB.68.085405