Explorando a termodinâmica e dinâmica do CO2 com modelos computacionais rígidos

Abstract

This study investigates the thermodynamic and dynamic behavior of carbon dioxide (CO2) under subcritical and supercritical conditions, covering a wide range of temperatures (228 to 500K) and pressures (1 to 150 atm). Using molecular dynamics (MD) simulations with well-established rigid models—EPM2 and TraPPE-small—structural, thermodynamic, and transport properties were analyzed. Both models showed good agreement with experimental data for the liquid-vapor coexistence curves, validating their applicability in describing CO2 under the simulated conditions. Radial distribution functions (RDF) revealed significant structural differences between the liquid, gas, liquid-gas coexistence, and supercritical phases, reflecting molecular reorganization in these regions. Mean squared displacement (MSD) analyses indicated a consistent increase in CO2 diffusivity with rising temperature at all simulated pressures (25.85, 44.41, 72.045, and 150 atm). For example, an increase from 5.2 × 10−9,m2/s at 300K to 1.8 × 10−8,m2/s at 500 K was observed at 150 atm, reflecting the enhanced molecular mobility in the supercritical regime. In addition, thermodynamic properties derived from response functions, such as the heat capacity at constant volume, adequately captured phase transitions, providing deeper insights into the fluid’s behavior. The results obtained highlight the effectiveness of MD simulations with rigid models in representing CO2 and their relevance for understanding phenomena under extreme conditions, as encountered in emerging technologies. Although this work is restricted to rigid models, its findings contribute to future investigations aimed at applications such as supercritical fluid extraction and preliminary studies in contexts related to Carbon Capture and Storage (CCS), provided they are validated by complementary approaches.