Cutoff Effects on the Equation of State of a Lennard–Jones Fluid: A Statistical Mechanical Analysis

Authors

Keywords:

Lennard–Jones fluid, Molecular Dynamics simulation, Equation of state, Virial pressure, Cutoff radius, Thermodynamic properties

Abstract

The Lennard–Jones (LJ) fluid is a standard model for linking microscopic intermolecular interactions to macroscopic thermodynamic behavior, yet its Molecular Dynamics (MD) predictions remain sensitive to potential truncation. This study uses equilibrium MD simulations to determine the equation of state (EOS) of a three-dimensional LJ fluid across reduced densities and temperatures. Pressure, potential energy, and compressibility factor were computed using the virial formulation, with emphasis on how cutoff radius and analytical tail corrections affect thermodynamic accuracy. The simulations reproduced expected LJ-fluid behavior: pressure increased nonlinearly with density, while the compressibility factor showed a transition from attraction-dominated states (Z<1)    to repulsion-dominated states (Z>1). Comparing rc=2.0σ, 2.5σ, and  3.0σ revealed systematic truncation errors that increased with density. At T = 1.2 and ρ = 0.8, pressure deviations between the smallest and largest cutoffs reached about 6–10%, while potential-energy deviations exceeded 10%. Tail corrections substantially reduced these errors and improved agreement with larger-cutoff simulations, although residual deviations persisted in dense, strongly correlated states. The findings show that cutoff treatment is a state-dependent thermodynamic bias in EOS reconstruction, not merely a computational setting.

Dimensions

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Published

2026-06-19

How to Cite

Cutoff Effects on the Equation of State of a Lennard–Jones Fluid: A Statistical Mechanical Analysis. (2026). Nigerian Journal of Applied Physics, 2(2), 49-65. https://doi.org/10.62292/njap-v2i2-2026-61

Issue

Vol. 2 No. 2 (2026): Nigerian Journal of Applied Physics - Vol. 2 No. 2

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Articles
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Copyright (c) 2026 Isaiah Eze Igwe, Moses A. Tyav

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How to Cite

Cutoff Effects on the Equation of State of a Lennard–Jones Fluid: A Statistical Mechanical Analysis. (2026). Nigerian Journal of Applied Physics, 2(2), 49-65. https://doi.org/10.62292/njap-v2i2-2026-61