Temperature-dependent Thermodynamic Behaviors of Carbon Fullerene Molecules at Atmospheric Pressure
Wen-Hwa Chen; Chun-Hung Wu; Hsien-Chie Cheng

Source CMC: Computers, Materials & Continua, Vol. 25, No. 3, pp. 195-214, 2011
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Keywords Thermal expansion coefficient, Phase transformation, Fullerene mole -cules, Molecular dynamics, Nosé-Hoover (NH) thermostat, Debye temperature
Abstract The study aims at investigating the linear and volumetric thermal expansion coefficients (CTEs) at temperature below the Debye temperature and phase transformation behaviors at atmospheric pressure of carbon fullerenes, i.e., C60, C70 and C80, through a modified Nosé-Hoover (NH) thermostat method incorporated with molecular dynamics (MD) simulation. The calculated results are compared with those obtained from the standard NH and "massive" NHC (MNHC) thermostats and also with the literature experimental and theoretical data. Results show that at temperature below the Debye temperature, the CTEs of the fullerene molecules would significantly decrease with a decreasing temperature and tend to become negative at temperature below 5K. The present results are much more consistent with the literature experimental and theoretical data, in contrast to the other two thermostat algorithms. Besides, it is found that C60 fullerene directly undergoes a solid-vapor phase transformation, instead of a solid-liquid phase transition, implying that the molecule will sublimate when heated rather than melt under atmospheric pressure. This phenomenon is coincident with that of graphite at pressures below 10MPa. The sublimation point of C60 fullerene is about 435020K, comparable to that of graphite in the range of about 4000-4500K at pressures below 10 MPa.
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