We report an atomistic molecular dynamics determination of the phase diagram of a rigid-cage model of C 36 . We first show that free energies obtained via thermodynamic integrations along isotherms displaying “van der Waals loops,” are fully reproduced by those obtained via isothermal-isochoric integration encompassing only stable states. We find that a similar result also holds for isochoric paths crossing van der Waals regions of the isotherms, and for integrations extending to rather high densities where liquid-solid coexistence can be expected to occur. On such a basis we are able to map the whole phase diagram of C 36 , with resulting triple point and critical temperatures about 1770 K and 2370 K, respectively. We thus predict a 600 K window of existence of a stable liquid phase. Also, at the triple point density, we find that the structural functions and the diffusion coefficient maintain a liquid-like character down to 1400–1300 K, this indicating a wide region of possible supercooling. We discuss why all these features might render possible the observation of the melting of C 36 fullerite and of its liquid state, at variance with what previously experienced for C 60 .

Communication: Phase diagram of C36 by atomistic molecular dynamics and thermodynamic integration through coexistence regions

ABRAMO, Maria Concetta;CACCAMO, Carlo;COSTA, Dino;MUNAO', GIANMARCO
2014

Abstract

We report an atomistic molecular dynamics determination of the phase diagram of a rigid-cage model of C 36 . We first show that free energies obtained via thermodynamic integrations along isotherms displaying “van der Waals loops,” are fully reproduced by those obtained via isothermal-isochoric integration encompassing only stable states. We find that a similar result also holds for isochoric paths crossing van der Waals regions of the isotherms, and for integrations extending to rather high densities where liquid-solid coexistence can be expected to occur. On such a basis we are able to map the whole phase diagram of C 36 , with resulting triple point and critical temperatures about 1770 K and 2370 K, respectively. We thus predict a 600 K window of existence of a stable liquid phase. Also, at the triple point density, we find that the structural functions and the diffusion coefficient maintain a liquid-like character down to 1400–1300 K, this indicating a wide region of possible supercooling. We discuss why all these features might render possible the observation of the melting of C 36 fullerite and of its liquid state, at variance with what previously experienced for C 60 .
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11570/3018000
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