CO2(aq) parameterization through free energy perturbation/monte carlo simulations for use in CO2 sequestration

Abstract

The gaseous and solution phase structures of CO2(aq) are investigated to aid in the development of CO2(aq) MM parameters for use in the CO2 sequestration modeling studies. Previous experimental and computational studies indicate two energetic minima for the interaction of a single CO2 and single water molecule, termed the T-structure and H-structure. For the determination of the energetic minima, ab initio calculations were performed, and the minima were found to have the respective values of-3.0 and-2.1 kcal/mol. From these ab initio calculations, a set of MM parameters were developed to reproduce the gas phase geometry and energetics. The gas-phase parameters were used as starting points in the aqueous phase parameter development, which used free energy perturbation Monte Carlo (FEP/MC) simulations to calculate the solubility of CO2 in aqueous solution as a function of temperature. Parameters were developed for CO2 to be used in the aqueous solution using the TIP3P, TIP4P, and TIP4P-Ew water models. The CO2(TIP4P-Ew) model was found to reproduce the solubility as a function of temperature to within 1% of the experimental solubility. Further testing of the CO2(TIP4P-Ew) model is done in the second part of this work, in which the solubility is calculated in several salt and brine solutions. © 2010 Springer Science+Business Media B.V.