Interaction-Range-Controlled Crossover from First-Order to Continuous Melting in Two-Dimensional Diplon Crystals — Code and Data

This deposit accompanies the article: P. S. Branicio, Interaction-Range-Controlled Crossover from First-Order to Continuous Melting in Two-Dimensional Diplon Crystals, APS Open Science (2026). https://doi.org/10.1103/r36h-bzv9 It contains the simulation/analysis/plotting code and the numerical data required to reproduce all four main-text figures and four supplemental figures. The full bulk-trajectory data (>150 GB) is not deposited here; the 798 MB included is sufficient to regenerate every figure and to verify every numerical claim in the article. Version 1.0.0 (5 May 2026) is the deposit as first submitted; a newer version (1.1.0, 19 August 2026) adds the Supplemental Secs. S6–S9 analysis scripts, the random-seed replicas and derived result files — see the version list on this page. Abstract: Molecular dynamics simulations of two-dimensional diplon crystals (electrons on helium films) reveal a melting crossover from first-order to continuous as film thickness d grows relative to lattice constant a. At small d/a, hysteresis persists at N = 40,000 alongside a strong Binder-cumulant anomaly. At large d/a, hysteresis vanishes and orientational correlations decay algebraically with η6 = 0.31 ± 0.04, near the KTHNY bound 1/4, consistent with continuous melting within the investigated system sizes and numerical resolution; disclination unbinding limits any hexatic phase to ΔT/Tm < 0.5%. The diplon system thus tunes 2D melting, relevant to electrons-on-helium quantum computing. Included: Complete simulation code (MD engine, Ewald summation, GPU kernels, MPI) KTHNY analysis pipeline (g₆, g_G, defect classification, AIC fitting, bootstrap error bars) Energy time series for every (d, N, T) point with both heating and cooling protocols, in .npy format Per-temperature configuration snapshots (one final snapshot per T) used for Voronoi and g₆(r) calculations in Figs 1, 2 Pre-computed KTHNY observables (η₆, ξ₆, |ψ₆|, six-fold fraction, free dislocation and disclination counts) in .npz format Not included (available from the author on request): Full production trajectories (traj_T*/ with 400 snapshots per T) — ~12 GB per (d, N) combination, ~150 GB total Equilibration-monitor .cfg files (cfg_monitor/) — internal-use diagnostic only