Solid--fluid equilibria for hard dumbbells via Monte Carlo simulation

Journal Article · Mon Jun 15 04:00:00 EDT 1992 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.462214· OSTI ID:7305962

Vega, C; Paras, E P.A.; Monson, P A ^[1]

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1. Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts 01003 (United States)

We present the results of a study of solid--fluid phase equilibria in systems of hard dumbbells for three values of the dumbbell bond length. Monte Carlo simulations were used to calculate the equation of state and Helmholtz free energy. Four orientationally ordered solid phases have been considered---the {alpha}-N{sub 2} structure and three different base centered monoclinic structures formed by the stacking of hexagonally packed layers that allow the dumbbells to achieve their maximum packing density. In addition, a face-centered-cubic (fcc) plastic crystal was studied for the system with the lowest bond length. The three base centered monoclinic structures have thermodynamic properties which are indistinguishable at the level of accuracy in our calculations. For longer bond lengths, the stable solid structure tends to be orientationally ordered base centered monoclinic. However, we also consider the stability of an aperiodic crystal for the case of dumbbells formed from tangent spheres. At lower bond lengths, the system freezes into a fcc plastic crystal which becomes unstable with respect to a base centered monoclinic structure at higher pressure. The transition between these solid phases is apparently first order. The behavior for the lowest bond length considered resembles that of nitrogen at high temperatures. Our results suggest that the {alpha}-N{sub 2} is not a stable crystal structure for hard dumbbell solids at any bond length, but does appear as a metastable phase in some cases.

• OSTI ID: 7305962
• Journal Information: Journal of Chemical Physics; (United States), Journal Name: Journal of Chemical Physics; (United States) Vol. 96:12; ISSN JCPSA; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360602* -- Other Materials-- Structure & Phase Studies
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
665000 -- Physics of Condensed Matter-- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BOND LENGTHS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CUBIC LATTICES
DIAGRAMS
DIMENSIONS
ELEMENTS
ELONGATION
ENERGY
EQUATIONS
EQUATIONS OF STATE
EQUILIBRIUM
FCC LATTICES
FLUIDS
FREE ENTHALPY
HARD-SPHERE MODEL
LENGTH
MECHANICAL PROPERTIES
MONOCLINIC LATTICES
MONTE CARLO METHOD
NITROGEN
NONMETALS
ORDER PARAMETERS
ORIENTATION
PHASE DIAGRAMS
PHYSICAL PROPERTIES
PLASTICITY
PRESSURE DEPENDENCE
SIMULATION
SOLIDS
THERMODYNAMIC PROPERTIES