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Detailed studies of the processes in low energy H irradiation of Li and Li-compound surfaces

Perspective article on plasma–material interaction at lithium-containing surfaces relevant to magnetic fusion: low-energy (1–100 eV) hydrogen irradiation of amorphous lithium oxide and lithium hydroxide surfaces is simulated and compared with prior work on amorphous Li and LiH, with emphasis on charge evolution and surface response.

Summary

The work addresses how hydrogen-fuel irradiation drives reflection, retention, chemical sputtering, and related processes on amorphous surfaces containing Li, O, and H—materials relevant to lithium-conditioned plasma-facing components. The study highlights electronegativity-driven polarization of Li and O and the need for reactive modeling that captures charge redistribution during collision cascades.

The J. Appl. Phys. abstract stresses side-by-side treatment of reflection, retention, and sputtering on the same footing for amorphous Li\(_2\)O and LiOH versus earlier amorphous Li and LiH benchmarks, and argues that time-dependent charging of Li/O/H during H irradiation can steer surface chemistry in ways that couple back to recycling, erosion, and plasma confinement modeling.

Methods

Interaction model (ReaxFF + EEM) (A/B)

Classical MD with ReaxFF bond order + electronegativity equalization in LAMMPS so charges evolve with geometry during cascades (Coulomb long-range included).

Amorphous surface preparation

Li\(_2\)O / LiOH slabs from fluorite Li\(_2\)O supercells: minimize, thermalize, relax to 2D periodic surfaces, then amorphize via heat/anneal cycles and final relaxation. Example LiOH cell ~5.6 × 5.6 × 12.2 nm, 29 735 atoms (~equimolar Li/O/H).

Impact protocol (B)

Incident H (also D/T context) 1–100 eV, varied incidence angles; Δt = 0.25 fs; 4 000–10 000 steps per run. Accumulate ~10³ impacts on ~3.5 × 3.5 nm\(^2\) patch for statistics.

1 — MD application (atomistic dynamics) — impact cascades

Engine / code: LAMMPS with ReaxFF + electronegativity equalization (EEM) for dynamical charges; Coulomb as in the article. System & composition: amorphous Li\(_2\)O and LiOH slab cells; example ~29 735 atoms in a 5.6 × 5.6 × 12.2 nm LiOH case (~equimolar Li/O/H). Boundaries / periodicity: 2D in-plane PBC for the bombarded surface patches (z non-periodic or as defined in the paper for the slab). Ensemble & thermostat for impacts: N/A in this short page—the article specifies whether NVE-like short trajectories and/or thermostat-attached baths are used in different stages. Barostat / hydrostatic pressure target: N/A for cascade bombardment in this note. Timestep: 0.25 fs; 4 000–10 000 steps/impact as in the Impact protocol above. Total wall-clock per impact: N/A — see paper. Temperature: ~300 K for prepared surfaces; beam energy 1–100 eV is the main driving variable, not a thermostat setpoint. External electric or magnetic field in MD: N/A (here the focus is H-beam PMI, not a macroscopic E-field in the MD). Coulomb / cutoffs as in the J. Appl. Phys. model. Enhanced sampling: N/A — direct cascade sampling.

2 — Force-field training

N/A — the work applies ReaxFF/EEM to Li–H–O surfaces; parameter provenance and validation context are in the article and prior work.

3 — Static QM

N/A — the paper compares to select quantum/classical references; full DFT production is not the core Methods line here.

Findings

Process competition

Reflection, retention, and chemical sputtering analyzed jointly and compared to prior amorphous Li / LiH studies.

Charging and PMI coupling

Time-dependent Li/O/H charges under irradiation alter erosion and recycling kinetics—relevant to lithium-conditioned plasma-facing components.

The abstract narrative also connects these atomistic mechanisms to tokamak PMI contexts where lithium coatings are used to modify impurity gettering and hydrogen recycling, motivating reactive models that retain charge evolution rather than fixed-partial-charge cascades alone.

Compared to prior amorphous Li and LiH sputtering data, the H-beam energy (1–100 eV), grazing incidence, and surface chemistry (Li\(_2\)O/LiOH) set a sensitivity map for chemical sputtering that EEM+ReaxFF is meant to reproduce; ReaxFF-level kinetic reaction barriers remain an inherent uncertainty relative to QCMD, and the open future direction in such PMI work is to extend the H-energy window and surface morphology with longer NVT-equilibrated patches—confirm all trends in the peer-reviewed pdf_path because this page does not capture every table.

Limitations

EEM-based charge updates approximate quantum mechanical polarization; the authors contrast this with full QCMD cost and note validation against selected quantum–classical results in related work. Low-energy chemical sputtering requires large cells at grazing incidence and higher impact energies to capture penetration depth, increasing cost.

Relevance to group

Co-authored by A. C. T. van Duin; extends ReaxFF/EEM lithium–oxygen–hydrogen surface chemistry for fusion PMI in collaboration with Princeton and Stony Brook groups.

Citations and evidence anchors

Reader notes (navigation)

  • Theme hubs: fusion / energy materials as covered elsewhere in the corpus when linked from indexes.