Solvent Dynamics Are Critical to Understanding Carbon Dioxide Dissolution and Hydration in Water

Simulations of carbon dioxide (CO2) in water may aidin understanding the impact of its accumulation in aquatic environmentsand help advance technologies for carbon capture and utilization (via,e.g., mineralization). Quantum mechanical (QM) simulations based onstatic molecular models with polarizable continuum solvation poorlyreproduce the energetics of CO2 hydration to form carbonicacid in water, independent of the level of QM theory employed. Onlywith density-functional-theory-based molecular dynamics and rare-eventsampling, followed by energy corrections based on embedded correlatedwavefunction theory (in conjunction with density functional embeddingtheory), can a close agreement between theory and experiment be achieved.Such multilevel simulations can serve as benchmarks for simpler, lesscostly models, giving insight into potential errors of the latter.The strong influence of sampling/averaging over dynamical solventconfigurations on the energetics stems from the difference in polarityof both the transition state and product (both polar) versus the reactant(nonpolar). When a solute undergoes a change in polarity during reaction,affecting its interaction with the solvent, careful assessment ofthe energetic contribution of the solvent response to this changeis critical. We show that static models (without structural sampling)that incorporate three explicit water molecules can yield far superiorresults than models with more explicit water molecules because fewerwater molecules yield less configurational artifacts. Static modelsintelligently incorporating both explicit (molecules directly participatingin the reaction) and implicit solvation, along with a proper QM theory,e.g., CCSD-(T) for closed-shell systems, can close the accuracy gapbetween static and dynamic models.

Automated summary

Simulations of carbon dioxide in water can help understand its impact on aquatic environments and advance carbon capture and utilization technologies. Only by using quantum mechanical simulations and rare-event sampling, combined with energy corrections, can the theoretical results closely match experimental data. These multilevel simulations can serve as benchmarks for simpler models and provide insights into their potential errors.