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  • Open Access

Using swapping layers in molecular dynamics simulations to drive structural equilibration far below Tg

Richard B. Stephens*

  • *Contact author: richst@sas.upenn.edu
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Phys. Rev. E 112, 065503 – Published 12 December, 2025

DOI: https://doi.org/10.1103/5dtg-jjx9

Abstract

The anomalous surface mobility exhibited by many slowly vapor-deposited molecular solids, and their simulated counterparts, allows annealing their structure and increasing their density down to Tdep≈0.85Tg. This work describes the design and characteristics of a simulation that uses a “swept swapping” technique designed to extend structural annealing to lower temperatures. Films are grown using size-dispersed attractive Lennard-Jones (L-J) potential spheres deposited onto their free surface and then equilibrated with a surface-following Monte Carlo swap region. The motion of that region combined with sphere size dispersion speeds structural relaxation by orders of magnitude compared to bulk swapping. Sphere size span and size step (25% and ∼2.5%, respectively) are sufficient to completely suppress crystallization and maintain a high swap acceptance rate. The regime revealed by this technique attains a high packing fraction, which is near that of an hexagonal-close-packed L-J crystal with no size-dispersion. Additional swapping refines its structure, at near constant density, maximizing short-range icosahedral order to levels higher than seen previously; the levels apparently limited only by the computing budget.

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Phys. Rev. E 112, 065503– Published 12 December, 2025
  • Received 28 February 2025
  • Revised 16 July 2025
  • Accepted 17 November 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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