ReaxFF Molecular Dynamics Simulation for the Graphitization of Amorphous Carbon: A Parametric Study

Area of Science:

• Materials Science
• Computational Chemistry
• Nanotechnology

Background:

• Graphitization of amorphous carbon is crucial for developing advanced carbon materials.
• Molecular dynamics simulations offer a powerful tool to study this transformation.
• Accurate force fields are essential for reliable simulation outcomes.

Purpose of the Study:

• To perform a parametric study of the ReaxFF force field for simulating amorphous carbon graphitization.
• To investigate the influence of initial configurations, time steps, temperatures, and ReaxFF parameter sets on simulation results.
• To assess the suitability of Chenoweth 2008 and Srinivasan 2015 parameter sets for modeling graphitic structure growth.

Main Methods:

• Parametric study using ReaxFF for molecular dynamics simulations.
• Varied simulation parameters: initial amorphous carbon configurations, time steps (<0.2 fs), temperatures, and ReaxFF parameter sets (Chenoweth 2008, Srinivasan 2015).
• Analysis of pair distribution functions, sp2 fraction, and structural evolution.

Main Results:

• A time step <0.2 fs is sufficient for ReaxFF simulations of carbon graphitization.
• Both parameter sets yield similar amorphous carbon networks at 300 K.
• Graphitization increases graphene fragment size and layer parallelism with temperature and time, forming structures near crystalline graphite.
• Graphitization leads to voids/pores due to more efficient atomic packing.
• The sp2 fraction increases significantly over time and with temperature, especially at lower densities (1.4 g/cm³).

Conclusions:

• Both Chenoweth 2008 and Srinivasan 2015 ReaxFF parameter sets are appropriate for simulating the growth of graphitic structures from amorphous carbon.
• Simulation parameters like temperature and annealing time critically influence the degree of graphitization and resulting structure.
• The study provides valuable insights for optimizing ReaxFF simulations in materials science research.