Gibbs Ensemble Monte Carlo for Reactive Force Fields to Determine the Vapor–Liquid Equilibrium of CO₂ and H₂O

Abstract

Absorption and reactive properties of fluids in porous media are key to the design and improvement of numerous energy related applications. Molecular simulations of these systems require accurate force fields that capture the involved chemical reactions and have the ability to describe the vapor−liquid equilibrium (VLE). Two new reactive force fields (ReaxFF) for CO 2 and H 2 O are developed, which are capable of not only modeling bond breaking and formation in reactive environments but also predicting their VLEs at saturation conditions. These new force fields include extra terms (ReaxFF-lg) to improve the long-range interactions between the molecules. For validation, we have developed a new Gibbs ensemble Monte Carlo (GEMC−ReaxFF) approach to predict the VLE. Computed VLE data show good agreement with National Institute of Standards and Technology reference data as well as existing nonreactive force fields. This validation proves the applicability of the GEMC−ReaxFF method to test new reactive force fields, and simultaneously it proves the applicability to extend newly developed ReaxFF force fields to other more complex reactive systems.

Reactive Grand-Canonical Monte Carlo Simulations for Modeling Hydration of MgCl2

“…E others can include other terms for specific systems, such as H bonds or extra dispersion interactions. 57 The bond order (BO) between atoms is described by a summation of empirical relations for the BO ij σ , BO ij π , and BO ij ππ bond, which depend on the distance r ij between the atoms i and j. 25…”

“…Furthermore, the MgCl 2 force field has proved itself useful for multiple hydration levels MgCl•nH 2 O (n = 0, 1, 2, 4, and 6), and the H 2 O force field is able to accurately capture both condensed and vapor phase under saturation conditions. 57 4.3.2. WCA Potential.…”

“…The terms E val , E tors , E pen , E under , E over , and E conj describe the valence and torsion contributions, “penalty” energies, under- and over-coordination, and conjugated systems, respectively. E others can include other terms for specific systems, such as H bonds or extra dispersion interactions . The bond order (BO) between atoms is described by a summation of empirical relations for the BO ij σ , BO ij π , and BO ij ππ bond, which depend on the distance r ij between the atoms i and j …”

“…To study the hydration of MgCl 2 hydrates, we used the ReaxFF force field developed by Pathak et al , in combination with the long-range corrected H 2 O ReaxFF force field . This force field was not explicitly trained to recreate the phase diagram of the salt; however, a transferable force field for TCM application should be able to recreate it.…”

“…To study the hydration of MgCl 2 hydrates, we used the ReaxFF force field developed by Pathak et al 12,13 in combination with the long-range corrected H 2 O ReaxFF force field. 57 This force field was not explicitly trained to recreate the phase diagram of the salt; however, a transferable force field for TCM application should be able to recreate it. Furthermore, the MgCl 2 force field has proved itself useful for multiple hydration levels MgCl•nH 2 O (n = 0, 1, 2, 4, and 6), and the H 2 O force field is able to accurately capture both condensed and vapor phase under saturation conditions.…”