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Title: Communication: Phase diagram of C{sub 36} by atomistic molecular dynamics and thermodynamic integration through coexistence regions

We report an atomistic molecular dynamics determination of the phase diagram of a rigid-cage model of C{sub 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{sub 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{sub 36} fullerite and of its liquid state, at variance with what previously experienced for C{sub 60}.
Authors:
; ; ;  [1]
  1. Dipartimento di Fisica e di Scienze della Terra, Università degli Studi di Messina and CNISM (Consorzio Nazionale Interuniversitario di Struttura della Materia) Viale F. Stagno d'Alcontres 31, 98166 Messina (Italy)
Publication Date:
OSTI Identifier:
22419850
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 141; Journal Issue: 9; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CRITICAL TEMPERATURE; DENSITY; DIFFUSION; FREE ENERGY; FULLERENES; ISOTHERMS; LIQUIDS; MELTING; MOLECULAR DYNAMICS METHOD; PHASE DIAGRAMS; SOLIDS; SUPERCOOLING; VAN DER WAALS FORCES