Mgr. Ivan Sukuba, PhD.

This thesis is a partial task within the research project on electron-impact ionisation cross sections for tungsten compounds relevant to thermonuclear reactor physics. Tungsten is the primary plasma-facing material in operating tokamaks (ASDEX Upgrade, WEST, EAST) and will be the main divertor material in ITER. Tungsten hydride clusters WH_m form from tungsten erosion by hydrogen isotopes and enter the scrape-off layer as impurity species; a 2026 systematic study (Fivet et al.) confirms that neutral tungsten and its simple compounds are the least-covered category in the OpenADAS database. Validated molecular geometries with correct spin states are the required first step — exactly this output constitutes the thesis. The focus on small WH clusters ensures experimental reference values are available for method validation within the two-semester scope.

• 1Literature review: DFT and semiempirical methods for transition metals; tungsten physics in fusion plasmas; atomic databases (IAEA ALADDIN, OpenADAS) and the data gap for WH₂ and above.
• 2Method validation: Spin scan (uhf = 0–6) for the isolated W atom; verify that spGFN2-xTB correctly predicts the ⁷S ground state (d⁴, uhf = 6) — an internal validity check before application to clusters.
• 3Structure generation: Systematic conformer search for WH and WH₂ using CREST; spin state scan (uhf = 0–5 for WH, 0–4 for WH₂); deduplication of resulting structures.
• 4DFT optimisation: Geometry optimisation at PBE/def2-SVP with Stuttgart effective core potentials (relativistic effects on W); extract W–H bond lengths; compare with experiment (WH: ~1.72 Å; WH₂: ~1.70 Å).

Key literature

• Cramer, C.J. (2004). Essentials of Computational Chemistry. 2nd ed. Wiley. [foundational textbook — DFT and semiempirical methods]
• Fivet, V. et al. (2026). Relativistic calculations of electron impact excitation cross-sections of neutral tungsten. arXiv:2603.02612. [data gap confirmation]
• Neugebauer, P. et al. (2023). High-throughput spin-state screening with spin-polarised extended tight-binding. J. Chem. Theory Comput. 19, 6208–6225.
• Pracht, P. et al. (2024). CREST — exploration of low-energy molecular chemical space. J. Chem. Phys. 160, 114110.
• Mašín, Z. et al. (2026). Effective Core Potentials for R-matrix calculations. J. Chem. Theory Comput. 22(4). [WH as sample calculation — PhD anchor]
• Andrae, D. et al. (1990). Stuttgart energy-adjusted pseudopotentials for second and third row transition elements. Theor. Chim. Acta 77, 123–141.
• Deutsch, H. et al. (2019). Electron impact ionisation cross sections for WH. J. Chem. Phys. 150, 044305.

This thesis is a partial task within the research projexton cosmic ray interactions with terrestrial and extraterrestrial materials. Forsterite (Mg₂SiO₄) is the dominant olivine mineral in meteorites, interplanetary dust, and surfaces of airless Solar System bodies. Space weathering — the progressive amorphization and defect formation under solar wind and cosmic ray bombardment — alters the infrared vibrational properties of forsterite observable with JWST/MIRI, which detected forsterite emission bands at 11.3 µm and 19.3 µm in the protoplanetary disc of Sz28 (Kanwar et al. A&A 2024) and monitors their variations in the JWST-DECO programme (from July 2024). A 2024 study (Hanafi et al. IUCrJ) explicitly modelled defect-rich forsterite by DFT as a Martian regolith analogue — a direct methodological precedent. The thesis computes the geometry and harmonic IR spectrum for both the pristine Mg₂SiO₄ cluster and a cluster with one Mg²⁺ vacancy (the most common defect type under ion bombardment) at the B3LYP/6-31G(d) level in Gaussian.

• 1Literature review: Mineralogy and crystallographic structure of Mg₂SiO₄; space weathering mechanisms of olivine; DFT cluster spectroscopy of silicates; astronomical IR observations by Spitzer, ISO, and JWST.
• 2Pristine cluster: Build a cluster approximation from crystallographic data; optimise geometry at B3LYP/6-31G(d); validate Si–O and Mg–O bond lengths against X-ray crystallography values.
• 3Defect cluster: Introduce a Mg²⁺ vacancy; optimise defect-containing geometry; characterise geometric relaxations around the vacancy site.
• 4IR spectra and comparison: Compute harmonic IR spectra for both clusters; identify vibrational modes altered by the vacancy; compare dominant band positions with JWST/MIRI and Spitzer observations.

Key literature

• Deer, W.A., Howie, R.A. & Zussman, J. (1997). Rock-Forming Minerals, Vol. 1A: Orthosilicates. Geological Society of London. [foundational crystallographic reference]
• Hanafi, M.I.J. et al. (2024). Defect-rich forsterite as a representative phase of Martian regolith. IUCrJ. [direct DFT methodological precedent]
• Kanwar, J. et al. (2024). JWST/MIRI forsterite bands at 11.3 and 19.3 µm in the disc of Sz28. Astron. Astrophys.
• Kaeufer, T. et al. (2026). JWST-DECO: temporal variations in mid-IR silicate features of T Tauri discs. MNRAS 548.
• Sogawa, H. et al. (2006). IR spectroscopic properties of crystalline forsterite. Astron. Astrophys. 451, L19–L22.
• Becke, A.D. (1993). Density-functional thermochemistry III. J. Chem. Phys. 98, 5648. [B3LYP functional]

This thesis is a partial task within the department's research programme on cosmic ray interactions with space materials, and is the direct methodological companion of Thesis C (DFT IR spectra of defect forsterite). Space weathering of asteroids and airless bodies converts crystalline olivine into a progressively amorphous, defect-rich phase. Oxygen atoms in the silicate lattice have the lowest threshold displacement energy (Td) compared with the heavier cations, making them the primary site of damage under low-energy ion bombardment. The thesis simulates displacement cascades initiated by a primary knock-on atom (PKA) on the oxygen sublattice at two energies — 0.5 keV (solar wind regime) and 5 keV (cosmic ray regime) — and determines Td(O). Simulations use LAMMPS with the Pedone et al. (Morse + Coulomb + ZBL) potential validated for forsterite in Couégnat et al. (Communications Materials 2026). MD-generated defect structures from this thesis can serve as input geometries for DFT calculations in Thesis C.

• 1Literature review: Radiation damage physics (displacement cascade theory, threshold displacement energy Td); interatomic potentials for silicates; space weathering of olivine; LAMMPS methodology. Collect Td values for MgO and SiO₂ analogues for later comparison.
• 2Supercell validation: Build and thermalise a crystalline Mg₂SiO₄ supercell (≥500 atoms) at 300 K with the Pedone+ZBL potential; validate density (3.22 g/cm³), lattice parameters, and RDF (O–O peak ~2.6 Å).
• 3Cascade simulations: Impart kinetic energy to an O PKA at 0.5 keV and 5 keV; NVE dynamics with variable timestep (max 0.003 nm/step); minimum 10 cascade trajectories per energy point; visualise in OVITO.
• 4Defect analysis: Quantify Frenkel pair production by the Wigner-Seitz cell method (OVITO): O vacancies and interstitials vs. PKA energy and cascade time. Determine Td(O) from low-energy cascades (10–100 eV).

Key literature

• Was, G.S. (2017). Fundamentals of Radiation Materials Science. 2nd ed. Springer. [foundational textbook — displacement cascade theory and Td]
• Couégnat, G. et al. (2026). Stress-induced amorphization as a transformation plasticity mechanism in forsterite. Communications Materials 7, 28. [Pedone potential in LAMMPS — direct precedent]
• Pedone, A. et al. (2006). New self-consistent empirical interatomic potential for oxides, silicates, and silica-based glasses. J. Phys. Chem. B 110, 11780.
• Nordlund, K. et al. (2018). Improving atomic displacement and replacement calculations with physically realistic damage models. Nature Communications 9, 1084.
• Malu, P.N. et al. (2024). MD simulations of displacement cascades in LiAlO₂ and LiAl₅O₈ ceramics. Scientific Reports 14, 1897. [cascade methodology in ionic ceramics]
• Thompson, A.P. et al. (2022). LAMMPS — a flexible simulation tool for particle-based materials modeling. Comput. Phys. Commun. 271, 108171.

This thesis is a partial task within the department's research programme on cosmic ray interactions with space materials. Water ice dominates the surfaces of outer Solar System bodies — comets and the icy moons of Jupiter (Europa, Ganymede) and Saturn. Interaction of solar wind protons with icy surfaces drives sputtering and contributes to exosphere formation. Sputtering yields are critical input parameters for surface evolution models; a 2025 study (Mishra et al. arXiv:2502.12780) explicitly notes that simultaneous species-resolved yields from a single experiment have not been previously reported. NASA's Europa Clipper (launched October 2024, Jupiter arrival April 2030) and ESA's JUICE require these data for exosphere modelling before arrival. The thesis simulates proton bombardment of an amorphous water ice slab at normal incidence at four energy points, computes the total sputtering yield, and compares with experimental data (Famá et al. 2008) and Sigmund's linear cascade theory. Simulations use LAMMPS with the TIP4P/2005 + ZBL potential (validated by Müller et al. 2024 for icy mixtures). The amorphous ice slab is prepared by quenching from the liquid phase.

• 1Literature review: Sputtering theory (linear cascade theory, Sigmund 1969); experimental measurements of water ice sputtering (Famá et al. 2008, Brown et al. 1984); MD modelling of ice in LAMMPS; physics of icy moons and Europa Clipper / JUICE missions.
• 2Ice preparation and potential: Prepare an amorphous water ice slab by quenching from liquid phase (300 K → 10 K; density 0.94 g/cm³); verify the amorphous structure via RDF (O–O peak ~2.8 Å). Implement the TIP4P/2005 + ZBL potential.
• 3Sputtering simulations: Simulate proton bombardment at normal incidence at 100 eV, 500 eV, 2 keV, and 5 keV; minimum 20 trajectories per energy point; identify and count sputtered atoms and molecules.
• 4Yield and comparison: Compute total sputtering yield (H₂O molecules per incident proton) as a function of energy; compare with Famá et al. (2008) and SRIM predictions; discuss in the context of Sigmund's theory.

Key literature

• Allen, M.P. & Tildesley, D.J. (2017). Computer Simulation of Liquids. 2nd ed. Oxford University Press. [foundational MD textbook]
• Famá, M. et al. (2008). Sputtering of water ice by low-energy ions. Surface Science 602, 156–161. [primary experimental benchmark]
• Sigmund, P. (1969). Theory of sputtering I. Phys. Rev. 184, 383–416. [foundational sputtering theory]
• Abascal, J.L.F. & Vega, C. (2005). A general purpose model for the condensed phases of water: TIP4P/2005. J. Chem. Phys. 123, 234505.
• Müller, J. et al. (2024). Solar Wind Irradiation of Methane and Water Ices: A Molecular Dynamics Approach. ACS Earth and Space Chemistry. [TIP4P+ZBL validated for icy mixtures]
• Mishra, Y.N. et al. (2025). Electron-induced chemistry of volatile species from water ice. arXiv:2502.12780. [data gap confirmation]
• Thompson, A.P. et al. (2022). LAMMPS. Comput. Phys. Commun. 271, 108171.