Carbon dioxide's gas-liquid transition: a Molecular Dynamics study

As the world grapples with increasingly stringent restrictions on greenhouse gas emissions, the need for industrial processes that prioritize environmental sustainability is paramount. Likewise, supercritical CO2 has applications in distinct technologies. In this context, a comprehensive understanding of CO2 molecules and their intricate behavior in the super and subcritical regimes is critical from a Basic and Applied Physics point of view.

In our study, we employ large scale Molecular Dynamics simulations to investigate the behavior of CO2 under various conditions. To capture the subtleties of molecular interactions, we used the EPM2 rigid model, which is known for its accuracy and reliability to depict the critical behavior, and compare it with the Trappe force field. Using the open-source package LAMMPS, we performed simulations in the NpT ensemble over a wide range of thermodynamic conditions, including both supercritical and subcritical pressures. By thoroughly exploring this extended parameter space, we aimed to uncover the nuances of CO2 thermodynamic, dynamic and structural behavior and shed light on its response to different thermodynamic conditions. our simulations successfully reproduced this behavior, confirming the accuracy of our approach.

Moreover, using Machine Learning approaches developed in our group, our studies have revealed significant structural and dynamic differences between these coexisting phases and the supercritical gas-like or fluid-like behavior. These differences play a critical role in our understanding about CO2 under different thermodynamic conditions.