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Helmholtz free energy; equation of state; quantum effects; perturbation theory

Using the Wigner-Kirkwood expansion and bare Lennard-Jones (LJ) (12-6) potential, an effectiveLJ potential is derived, which includes the quantum effects through the expressions of the effective diameter∂(T, λ) and well-depth $$\bar \varepsilon \left( {T,\lambda } \right)$$(T, λ). We use theWCA perturbation theory to calculate the free energy and pressure for theLJ and effectiveLJ potentials. Simple analytic expressions are given for the reference system and the first order correction calculated. The results are quite good at high density. The quantum effects on the free energy and pressure are also discussed.

T P Singh^{1 2} S K Sinha¹

1. Department of Physics, L S College, Bihar University, Muzaffarpur - 842 001, India
2. Department of Physics, J N College, Dighwara, India

Published

December 1985

Manuscript received

17 April 1985

Manuscript revised

17 September 1985