Comprehensive study of the thermodynamic properties of fullerene C₆₀ along the liquid–vapour coexistence

Abstract

We present a theoretical model for calculating the thermodynamic properties of liquid C₆₀ by means of an improved equation of state (EOS), in which the particles interact via pairwise interaction composed of hard-core plus suitable linear combinations of three Yukawa functions. The proposed EOS provides simple analytical expressions for Helmholtz free energy and pressure, which are the basic ingredients to compute the liquid–vapour coexistence curve of C₆₀ as well as all other thermodynamic properties for the bulk liquid and vapour phases. The comparisons with computer simulation results, based on Girifalco potential, suggest the importance of treating the attractive tail of the potential accurately. It is to be noted that the obtained results of the thermodynamic properties along the binodal curve of C₆₀ exhibit interesting features; in particular, the vapour phase shows abnormal behaviour of its isothermal compressibility and configurational heat capacity. The estimated critical parameters T_c = 2008.8 K, ρ_c = 0.50 nm⁻³ and P_c = 54.8 bars are in good agreement with NVT-Monte Carlo simulation predictions. The critical parameters of C₆₀ are compared with those of liquid metals, non-metals and some hydrocarbons.

Keywords:

• carbon fullerene C₆₀
• thermodynamic properties of C₆₀
• equation of state of C₆₀
• liquid–vapour coexistence of C₆₀
• C₆₀ pair potential

Acknowledgements

The authors are grateful to the Sultan Qaboos University for the Research Project IG/Sci/Phys/07/04. M. Bahaa Khedr would like to thank SQU for hospitality and substantial financial support for completing this work.