Systems of C60 molecules inside (10,10) and (15,15) nanotube:: A Monte Carlo study -: art. no. 085405

We use Monte Carlo simulations to investigate properties of systems of C-60 molecules inside (10,10) and (15,15) nanotubes. In the case of the (10,10) nanotube, 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 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 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 (>95%) do not show this peak and "melt" differently.