Thermal conductivity of carbon dioxide from non-equilibrium molecular dynamics: A systematic study of several common force fields

We report a systematic investigation of the thermal conductivity of various three-site models of carbon dioxide (CO2) using nonequilibrium molecular dynamics in the temperature range 300–1000 K and for pressures up to 200 MPa. A direct comparison with experimental data is made. Three popular CO2 force fields (MSM, EPM2, and TraPPE) and two flexible models (based on EPM2) were investigated. All rigid force fields accurately predict the equation of state for carbon dioxide for the given range of variables. They can also reproduce the thermal conductivity of CO2 at room temperature and predict a decrease of the thermal conductivity with increasing temperature. At high temperatures, the rigid models underestimate the thermal conductivity.Process and EnergyMechanical, Maritime and Materials Engineerin

Thermodynamic characterization of two layers of CO2 on a graphite surface

We find by examination of density profiles that carbon dioxide adsorbs on graphite in two distinct layers. We report the activity coefficient, entropy and enthalpy for CO2 in each layer using a convenient computational method, the Small System Method, thereby extending this method to surfaces. This opens up the possibility to study thermodynamic properties for a wide range of surface phenomena.Process and EnergyMechanical, Maritime and Materials Engineerin

Simulating CO2 adsorption and diffusion on a graphite surface

We performed classical molecular dynamics (MD) simulation to understand the mechanism of CO2 adsorption and transport on graphite surface. The temperature of the system in our simulation was in the range 300-500K. The simulation data show that there are two layers of CO2 molecules absorbed on the surface. These two layers have a different behavior. The first CO2 layer is isolated as it does not exchange molecules with the second layer and is liquid-like, while the second layer exchanges molecules with the gas phase. The layers are separate thermodynamic systems. We use the simple Langmuir model to fit the adsorption isotherm for the second layer. The enthalpy of adsorption is calculated ?H0 = -16 kJ/mol. This value is in good agreement with experimental data of adsorption of CO2 on activated carbon. Along the graphite surface, the diffusion coefficient of CO2 in the first layer and the second layer are roughly of 10-11 m2/s, 10-10 m2/s respectively. These values are much smaller than for H2.Process and EnergyMechanical, Maritime and Materials Engineerin

Partial molar enthalpies and reaction enthalpies from equilibrium molecular dynamics simulation

We present a new molecular simulation technique for determining partial molar enthalpies in mixtures of gases and liquids from single simulations, without relying on particle insertions, deletions, or identity changes. The method can also be applied to systems with chemical reactions. We demonstrate our method for binary mixtures of Weeks-Chandler-Anderson particles by comparing with conventional simulation techniques, as well as for a simple model that mimics a chemical reaction. The method considers small subsystems inside a large reservoir (i.e., the simulation box), and uses the construction of Hill to compute properties in the thermodynamic limit from small-scale fluctuations. Results obtained with the new method are in excellent agreement with those from previous methods. Especially for modeling chemical reactions, our method can be a valuable tool for determining reaction enthalpies directly from a single MD simulation.Process and EnergyMechanical, Maritime and Materials Engineerin