Effects of van der Waals Interaction on N₂ Adsorption on Carbon Nanotubes: Proposal for New Force Field Parameters

The separation of carbon dioxide (CO₂) from nitrogen gas (N₂) in flue gas has become an emerging strategy to mitigate climate change. Molecular simulations are valuable to provide insights for the gas separation process. A careful choice of force fields is required to avoid unrealistic predictions of thermodynamic properties. Most studies use Lorentz-Berthelot combining rules (LB) to obtain the interaction between different species. In this context, we verified how accurate LB is in describing the interaction of N₂ molecules and carbon nanostructures by comparing the interaction energies of LB with those from density functional theory (DFT) calculations. Carbon nanomaterials were selected because they are considered promising materials to perform N₂/CO₂ separation. The results show that the LB underestimates the interaction energies and affects the prediction of the fundamental properties of solid-fluid interfacial interactions. To overcome this, we parametrized a Lennard-Jones potential using DFT and considering van der Waals interactions. The proposed potential shows good transferability and agreement with ab initio calculations. Molecular simulations were performed to verify the effects of employing LB in predicting the amount of nitrogen gas adsorbed in carbon nanotubes (CNTs). LB predicts a lower density within them. Our results suggest that LB leads to different adsorption properties.