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

This deposit accompanies the manuscript:

P. S. Branicio, Interaction-Range-Controlled Crossover from First-Order to Continuous Melting in Two-Dimensional Diplon Crystals (2026).

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 paper.

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. For large d/a, hysteresis vanishes and orientational correlations decay algebraically with η6 = 0.31 ± 0.04, near the KTHNY bound 1/4; 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, defect counts, |ψ₆|, susceptibility) 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