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ReaxFF reactive force field for exploring electronically switchable polarization in Zn1−xMgxO ferroelectric semiconductors

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Authority of statements

Prose sections below (Summary, Methods, Findings, etc.) are curated summaries of the publication identified by doi, title, and pdf_path in the front matter above. They are not new primary claims by this wiki.

Summary

Wurtzite-derived ZnO can host ferroelectric-like polar order when alloyed and strained, offering a non-perovskite route to switchable polarization in wide-gap oxides, but quantitative modeling must connect dopant chemistry to domain stability and coercivity. The paper parametrizes a ReaxFF model for Zn₁₋ₓMgₓO, a non-perovskite ferroelectric semiconductor, using density-functional theory (DFT) training data spanning bonding environments relevant to wurtzite-derived polar distortions, then uses large-scale MD to study polarization hysteresis, coercive fields, and Mg distribution effects in nanoscale films. The abstract motivates the force-field effort by noting that first-principles studies of doped ZnO ferroelectricity are computationally costly at device-relevant scales, whereas ReaxFF enables field-driven switching trajectories in larger cells. Readers should treat reported remnant polarization magnitudes, critical thickness estimates, and coercive-field trends as model predictions to be cross-checked against DFT and experiment in the full article and supporting information.

Methods

ReaxFF parameterization (A)

DFT database for Zn–Mg–O environments supporting wurtzite-derived polar distortions.

Field-driven reactive MD (B)

Thin-film-like supercells; E-field switching sweeps; Mg x, clustered vs random dopant layouts, T; outputs include P(E) hysteresis and remanent P.

Protocol sensitivity: coercive field, critical thickness—verify thermostat, damping, ramp against Computational Details/SI in papers/Sepehrinezhad_ZnMgO_JPCC_2024.pdf.

Electrostatics in field-driven runs. Field-coupled ReaxFF simulations require consistent charge equilibration frequency and damping choices when E-field magnitudes change; the article’s Computational Details specify how thin-film supercells treat vacuum padding, fixed bottom layers (if any), and ramp schedules for polarization reversal.

MD application (E-field, ferroelectric switching). LAMMPS+ReaxFF in NVT (or as stated) with PBC in-plane for wurtzite Zn\(_{1-x}\)Mg\(_x\)O-like thin-film supercells; system size and Mg doping layouts in J. Phys. Chem. C 2024. Time step (fs), equilibration/production (ps/ns), Nosé–Hoover thermostat and damping, and E-field sweeps in V/nm or MV/cm (see article) are N/A to restate line-by-line here. N/A—NPT barostat if runs are constant-volume and isotropic stress is not targeted; N/A—metadynamics. Temperature is varied to study coercive trends. Hydrostatic pressure N/A for standard NVT E-field protocols in the summary.

Findings

Ferroelectric switching appears at a critical thickness near ~10 nm with residual polarization ~100 μC/cm² (order of magnitude as reported). Higher Mg substitution correlates with lower coercive field in the model study. Coercive field decreases with increasing temperature. Clustered Mg increases coercive field relative to more uniform arrangements, whereas random Mg lowers it versus uniform distributions—highlighting microstructural control of switching in doped ZnO-class ferroelectrics.

Limitations

Electronic polarization in ReaxFF is classical; quantitative agreement with DFT or experiment for absolute P(E) curves should be checked against the full article and SI.

Relevance to group

Extends ReaxFF into ferroelectric oxide semiconductors beyond perovskites, co-authored by van Duin and Dabo.

Citations and evidence anchors

  • DOI: 10.1021/acs.jpcc.4c02233
  • J. Phys. Chem. C 128, 12534–12543 (2024)
  • normalized/extracts/2024alireza-sepehrinezha-j-phys-chem-reaxff-reactive_p1-2.txt

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