Negative Expansion in Two-Molecule System with the Step Function outside the Hard Sphere Wall in a Spherical Cell

Yosuke KATAOKA* and Yuri YAMADA

Department of Materials Chemistry, College of Engineering, Hosei University
3-7-2 Kajino-cho, Koganei, Tokyo 184-8584

(Received: June 22, 2005; Accepted for publication: November 30, 2005; Published on Web: March 3, 2006)

The canonical ensemble partition function is obtained for a two-molecule system with the repulsive step function outside the hard sphere wall in a spherical cell. Fluid-fluid phase transition-like behavior is evident at low temperatures. The spinodal line is obtained in the (V, T) domain and a negative expansion coefficient is found in the stable state. The theoretical pVT relationship is confirmed through Monte Carlo simulations. The periodic 108-molecule system examined by Monte Carlo simulations also provides a qualitatively similar pVT relationship to the two-molecule system.

Keywords: Negative Expansion, Canonical ensemble partition function, Repulsive step function, Monte Carlo simulations, Spinodal line

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