Nanoindentation of monolayer Tin+1CnTx MXenes via atomistic simulations: The role of composition and defects on strength
Summary¶
Plummer, Anasori, Gogotsi, and Tucker (Computational Materials Science 157 (2019) 168–174; DOI 10.1016/j.commatsci.2018.10.033; available online 8 November 2018) simulate nanoindentation of oxygen-terminated Ti₃C₂O₂ and Ti₂CO₂ MXene monolayers with ReaxFF in LAMMPS to extract Young’s moduli and quantify softening from titanium and carbon vacancies. The abstract in the extract states that Young’s moduli for pristine Ti₃C₂O₂ and Ti₂CO₂ are 466 GPa and 983 GPa, respectively, and that a defective Ti₃C₂O₂ sample with 1% V_Ti and 10% V_C yields 386 ± 31 GPa, mirroring experimental sensitivity of MXenes to defects and comparing defect-containing Ti₃C₂O₂ to graphene oxide moduli for solution-processed 2D materials. The introduction recounts MXenes’ 2011 discovery, selective etching of MAX phases, and application spaces (energy storage, composites, membranes, sensors), motivating fundamental mechanical characterization.
Methods¶
1 — MD application (simulated nanoindentation). ReaxFF (Ti₃C₂Tₓ-compatible parametrization cited in Computational Materials Science) is used in LAMMPS with QEq-style charge equilibration and documented nonbond cutoffs (see article). PBC: periodic in-plane monolayer cells of oxygen-terminated Ti₃C₂O₂ and Ti₂CO₂; a rigid spherical indenter (10 nm diameter) advances at 10 m·s⁻¹ along the surface normal while recording force–displacement curves (OVITO visualization). Ensemble: NVT at 1 K to suppress thermal noise during modulus extraction. Timestep: 0.25 fs. Defect models: additional Ti₃C₂O₂ cells include ~1 % Ti vacancies and ~10 % C vacancies simultaneously as in the abstract. Duration / staging: follow the staged relaxation + indentation protocol in the paper (exact ps/ns windows in Methods/figures). Thermostat / temperature control: same protocol as the sibling page: 1 K held during indentation in the canonical (NVT) ensemble with details in papers/ReaxFF_others/Plummer_Anasori_Gogotsi_MXene_indentation_2019.pdf. Barostat / pressure: N/A — NVT indentation without hydrostatic NPT barostat control. Electric fields / enhanced sampling: N/A — not used.
2 — Force-field training. N/A — applies a published MXene ReaxFF parametrization with DFT training heritage referenced in the article.
3 — Static QM. N/A — not a DFT-only study.
Corpus / duplicate note: same DOI and simulation definition as 2018plummer-computationa-nanoindentation-monolayer; only pdf_path / SHA differ in this manifest.
Findings¶
Outcomes: reported Young’s moduli are ~466 GPa (pristine Ti₃C₂O₂) and ~983 GPa (pristine Ti₂CO₂); combined Ti + C vacancies reduce Ti₃C₂O₂ to ~386 ± 31 GPa in the quoted defective model.
Comparisons: defective Ti₃C₂O₂ is compared to graphene oxide moduli cited for solution-processed 2D materials.
Sensitivity: composition (n+1,n family member) and vacancy loading strongly shift stiffness extracted from indentation slopes.
Limitations: 1 K sampling suppresses thermal effects; rigid indenter + classical ReaxFF omit explicit electronic plasticity.
Corpus honesty: moduli and defect percentages are taken from the abstract on pdf_path; verify against Comput. Mater. Sci. tables.
Limitations¶
Low temperature (1 K) suppresses thermal phonon effects; the rigid indenter and empirical potential omit explicit electronic plasticity and may over- or under-estimate defect interactions at room temperature.
Indentation at cryogenic temperatures isolates mechanical stiffening from thermally activated defect migration, which is useful for comparing potentials but diverges from room-temperature experiments unless thermal effects are explicitly reintroduced in follow-on work. Readers should treat the quoted moduli as comparative screening metrics within the article’s model assumptions rather than as direct predictions of ambient nanoindentation experiments on exfoliated MXene flakes.
Relevance to group¶
Demonstrates ReaxFF-based indentation workflows for MXene mechanical screening relevant to 2D carbide mechanics literature in the knowledge base.
Reader notes (navigation)¶
- Canonical duplicate: 2018plummer-computationa-nanoindentation-monolayer
- reaxff-family