Structural and dynamical properties predicted by reactive force fields simulations for four common pure fluids at liquid and gaseous non-reactive conditions

Abstract

Four common pure fluids were chosen to elucidate the reliability of reactive force fields in estimating bulk properties of selected molecular systems: CH4, H2O, CO2 and H2. The pure fluids are not expected to undergo chemical reactions at the conditions chosen for these simulations. The 'combustion' ReaxFF was chosen as reactive force field. In the case of water, we also considered the 'aqueous' ReaxFF model. The results were compared to data obtained implementing popular classic force fields. In the gas phase it was found that simulations conducted using the 'combustion' ReaxFF formalism yield structural properties in reasonable good agreement with classic simulations for CO2 and H2, but not for CH4 and H2O. In the liquid phase 'combustion' ReaxFF simulations reproduce reasonably well the structure obtained from classic simulations for CH4, degrade for CO2 and H2, and are rather poor for H2O. In the gas phase the simulation results are compared to experimental second virial coefficient data. The 'combustion' ReaxFF simulations yield second virial coefficients that are not sufficiently negative for both CH4 and CO2, and slightly too negative for H2. The 'combustion' ReaxFF parameterization induces too strong an effective attraction between water molecules, while the 'aqueous' ReaxFF yields a second virial coefficient for water that is in reasonable agreement with experiments. The 'combustion' ReaxFF parameterization yields acceptable self-diffusion coefficients for gas-phase properties of CH4, CO2 and H2. In the liquid phase the results are good for CO2, while the self-diffusion coefficient predicted for liquid CH4 is slower, and that predicted for liquid H2 is about 9 times faster than those expected based on classic simulations. The 'aqueous' ReaxFF parameterization yields good results for both the structure and the diffusion of both bulk liquid and bulk vapour water.

Supercritical CO2 Effects on Calcite Wettability: A Molecular Perspective

“…Each model has advantages and disadvantages. The SPC/E model yields good results for structure and dynamics of bulk liquid water at ambient conditions − and for static dielectric constant over a very wide range of temperatures and densities, but it underestimates water viscosity and fails to reproduce experimental vapor pressure, as well as other thermodynamic properties at critical and supercritical conditions . The SPC model is successful at reproducing the liquid–vapor coexistence curve and vapor pressure, , but it over-predicts the diffusion coefficient .…”

Partial CO2 Reduction in Amorphous Cylindrical Silica Nanopores Studied with Reactive Molecular Dynamics Simulations

“…[57][58][59] Recently, we found that the ReaxFF parameterisation can predict structural and transport properties of nonreactive pure fluids (CH4, CO2, H2O, and H2). 60 However, our results showed that the agreement with both classical simulations and experiments depends strongly on the fluid considered and on the thermodynamics conditions simulated.…”

“…ReaxFF parameters are obtained by fitting against training datasets containing quantum mechanical simulation results and experimental data. Accurate ReaxFF parameterizations have been applied to a wide range of reactive systems, including combustion processes, − the shock-induced chemistry of high-energy materials, − nanomaterials, − catalysts, − and also electrochemical phenomena. − Recently, we found that the ReaxFF parameterization can predict structural and transport properties of nonreactive pure fluids (CH 4 , CO 2 , H 2 O, and H 2 ) . However, our results showed that the agreement with both classical simulations and experiments depends strongly on the fluid considered and on the thermodynamics conditions simulated.…”

Competitive adsorption and reduced mobility: N-octane, CO2 and H2S in alumina and graphite pores

“…The MSD plots are shown in Figure 9. It should be noted that simulation box size affects diffusion results estimated from MD simulations [57][58][59] because of finite-size effects due to the implementation of the periodic boundary conditions [60]. An analytical correction proportional to N −1/3 (N being number of molecules in the simulated box) has been proposed to account for such effects.…”