Eur. Phys. J. B (2012) 85: 193
https://doi.org/10.1140/epjb/e2012-20908-6

Regular Article

Analytic equation of state and thermodynamic properties for solid FCC C₆₀ over a wide range of pressures and temperatures

¹ School of Electronic information Engineering, University of Chengdu, Chengdu, Sichuan 610106, P.R. China
² Department of Applied Physics, University of Electronic Science and Technology, Chengdu, Sichuan 610054, P.R. China
³ Department of Physics, A’ ba Teachers College, Chengdu, Sichuan 611741, P.R. China

^a e-mail: yangweiuestc@yahoo.cn

Received: 7 November 2011
Received in final form: 13 April 2012
Published online: 12 June 2012

Abstract

As an analytic approximation to the free volume theory (FVT), the analytic mean field potential (AMFP) approach is applied to the multi-exponential model solid. The analytic expressions for the equation of state (EOS) and thermodynamic quantities are derived. The formalism for the case of the double-exponential (DE) model is applied to the solid fcc C₆₀. The four potential parameters are determined by fitting the experimental data of cohesive energy, lattice constant and compression curve of solid C₆₀. The numerical results calculated show that the Girifalco potential is too hard and gives compression curve prominently deviated from experiments at high pressure, whereas the DE potential can well describe the thermo-physical properties of C₆₀ system within wide pressure range. The calculated variation of lattice constant versus temperature relationship and compression curve for solid C₆₀ by using the DE potential agree well with experimental data available. Especially the AMFP with DE potential predicted that the fcc C₆₀ solid is stable up to 2440 K, the spinodal temperature, in good agreement with the result from molecular dynamic (MD) simulation. The AMFP is a useful approach to consider the anharmonic effects at high temperature for solid C₆₀.