Molecular Dynamics Simulation of Transport and Structural Properties of CO₂ Using Different Molecular Models

Abstract

The diffusion coefficients (<i>D</i>_s), viscosities (η), and structural properties of carbon dioxide (CO₂) have been studied using molecular dynamics (MD) simulation. Three fully flexible models (MSM-flex, EPM2-flex, and TraPPE-flex) from the literature are used to model CO₂. Present simulations have extended the temperature range from 223 K to 450 K and pressures up to 200 MPa for the first time. Generally, the simulation results show a good agreement with the experimental ones. The overall satisfaction of the EPM2-flex model is found to be the best, with an average absolute relative deviation of 6.83 % for <i>D</i>_s and of 2.87 % for η, respectively. However, the TraPPE-flex model performs best at low temperatures below 273 K. Meanwhile, the lifetime of CO₂ molecules in the first solvation shell (τ^s) is calculated, and the qualitative correlation between τ^s and <i>D</i>_s as well as τ^s and η is discussed. Finally, the structures of CO₂ fluid in different thermodynamic states are investigated by calculating radial distribution functions and using a clustering algorithm