Skip to content

Phase transitions of ordered ice in graphene nanocapillaries and carbon nanotubes

Summary

ReaxFF molecular dynamics, following grand-canonical Monte Carlo initialization of confined water, maps ice and water in graphene nanocapillaries and single-walled carbon nanotubes. The work emphasizes AA-stacked multilayer square ice with interlayer hydrogen bonding, first-order versus continuous melting (and critical-point-like behavior) depending on density and layer count, elevated solid–liquid transition temperatures in CNTs compared with 273 K, and enhanced proton/hydroxyl transport (up to roughly several-fold over bulk at 300 K in ordered confinement).

Methods

1 — MD application (confined water + ice). Grand-canonical Monte Carlo (GCMC) at fixed liquid-water chemical potential initializes confined structures (SI details). Production runs use ReaxFF molecular dynamics with 0.10 fs timestep and Nosé–Hoover thermostat (10 fs coupling) under the constant-volume protocols described in Sci. Rep. (the article quotes 1 atm target conditions while keeping cell metrics fixed during heating/melting segments—treat as the paper’s documented NVT-like melting workflow rather than inventing a separate barostat here). PBC: three-dimensional PBC for graphene nanocapillaries and CNT confinement models. System sizes / atom counts: follow figure/table construction in the article (SI for exact counts). Temperature: melting scans span 230–400 K continuous regimes discussed for certain square-ice stacks, include 300 K transport analyses for confined 1D/2D ice, and use broader heating windows tabulated in Sci. Rep. figures. Duration: nanosecond-class cumulative sampling is referenced for selected melting scans in the article/SI (use the PDF for exact segment lengths). Barostat during melting sweeps: N/A — not separated as NPT production in the excerpted description. Pressure / stress control: 1 atm referenced for thermostatized melting studies; no external electric field. Enhanced sampling: N/A — aside from GCMC pre-equilibration.

2 — Force-field training. N/A — uses published ReaxFF water/carbon chemistry.

3 — Static QM. N/A — not an AIMD-first study.

Duplicate PDF note: this slug mirrors 2018raju-scientific-r-phase-transitions with an alternate pdf_path (papers/Raju_Scientific_Reports_2018_online.pdf).

Findings

Outcomes / mechanisms: ReaxFF reproduces AA-stacked multilayer square ice in graphene nanocapillaries with interlayer H-bonds, contrasting some older AB-stacked classical pictures. Melting signatures differ: bilayer hexagonal ice shows first-order-like jumps, whereas some square-ice stacks show continuous energy evolution over ~230–400 K windows discussed in the text. CNT confinement raises melting temperatures above 273 K, discussed alongside Raman literature constraints. Proton/hydroxyl mobilities can exceed bulk by up to several-fold at 300 K in ordered confinement.

Comparisons: stacking and melting behavior are compared to prior classical models and selected experiments cited in the paper.

Sensitivity: confinement geometry (2D slit vs 1D tube) steers polymorph selection and melting classification.

Limitations: ReaxFF bulk-water errors propagate to phase boundaries; sampling length affects sharp vs gradual melting.

Corpus honesty: this slug is an alternate publisher PDF for the same Scientific Reports article as 2018raju-scientific-r-phase-transitions (papers/Raju_Scientific_Reports_2018.pdf); scientific content matches that entry. Confirm numbers against whichever VOR/SI PDF you cite externally.

Limitations

ReaxFF bulk-water benchmarks deviate from experiment and ab initio references in some limits; phase boundaries depend on confinement geometry, water model, and sampling length. Maintaining two article PDFs in the corpus is for manifest convenience only.

Relevance to group

Adri van Duin co-authorship; extends ReaxFF studies of nanoconfined water on carbon for retrieval alongside 2018raju-scientific-r-phase-transitions.

Citations and evidence anchors

Reader notes (navigation)