Reactive molecular dynamics simulation for isotope-exchange reactions in H/D systems: ReaxFF_HD development.

Area of Science:

• Plasma Physics
• Computational Chemistry
• Materials Science

Background:

• Hydrogen-deuterium (H/D) isotope-exchange reactions are crucial in plasma environments.
• Accurate modeling of these reactions requires robust computational potentials.
• Understanding ion formation pathways is key to controlling plasma composition.

Purpose of the Study:

• To parameterize a ReaxFF potential (ReaxFFHD) for H/D isotope-exchange reactions.
• To simulate reactive molecular dynamics of H/D mixtures in plasma.
• To analyze the formation of tri-atomic molecular ions (H3+, D3+, H2D+, D2H+) and isotope effects.

Main Methods:

• Quantum mechanics (QM) calculations for training data generation.
• Parameterization of the ReaxFFHD potential using QM data.
• 1 nanosecond reactive molecular dynamics simulations of H/D mixtures.
• Analysis of reaction pathways and product distributions.

Main Results:

• The ReaxFFHD potential accurately models H/D isotope-exchange reactions and shows excellent transferability.
• Simulations identified intermediate molecules (H2, D2, HD) forming tri-atomic molecular ions as primary products.
• A preference for deuterium in molecular ions was observed, linked to lower zero-point energy.

Conclusions:

• The ReaxFFHD potential is a reliable tool for simulating isotope-exchange reactions in hydrogen plasma.
• Tri-atomic molecular ions are favored products, with deuterium enrichment influenced by zero-point energy differences.
• This work provides insights into plasma chemistry and isotope effects.