Development and application of ReaxFF methodology for understanding the chemical dynamics of metal carbonates in aqueous solutions

• Published in: Physical chemistry chemical physics : PCCP 2022-02, Vol.24 (5), p.3322-3337
• Main Authors: Dasgupta, Nabankur, Chen, Chen, van Duin, Adri C. T
• Format: Article
• Language: English
• Subjects: Ambient temperature; Angular distribution; Aqueous solutions; Bicarbonates; Calcium ions; Carbonates; Clusters; Deceleration; Diffusion coefficient; Equations of state; Heat of formation; Heat of reaction; Mathematical analysis; Molecular dynamics; Nucleation; Parameters; Protonation; Quantum mechanics; Residence time distribution; Self diffusion; Sodium; Solvation; Vibrational spectra
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d1cp04790f

A new ReaxFF reactive force field has been developed for metal carbonate systems including Na + , Ca 2+ , and Mg 2+ cations and the CO 3 2− anion. This force field is fully transferable with previous ReaxFF water and water/electrolyte descriptions. The Me-O-C (Me = metal) three-body valence angle parameters and Me-C non-reactive parameters of the force field have been optimized against quantum mechanical calculations including equations of state, heats of formation, heats of reaction, angle distortions and vibrational frequencies. The new metal carbonate force field has been validated using molecular dynamics simulations to study the solvation and reactivity of metal and carbonate ions in water at 300 K and 700 K. The coordination radius and self-diffusion coefficient show good consistency with existing experimental and simulation results. The angular distribution analysis explains the structural preference of carbonate ions to form carbonates and bicarbonates, where Na + predominantly forms carbonates due to weaker angular strain, while Ca 2+ and Mg 2+ prefer to form bicarbonate monodentate in nature. Residence time distribution analyses on different systems reveal the role of ions in accelerating and decelerating the dynamics of water and carbonate ions under different thermodynamic conditions. The formation and dissolution of bicarbonates and carbonates in solution were explored on the basis of the protonation capability in different systems. The nucleation phenomenon of metal carbonates at ambient and supercritical conditions is explained from the perspective of cluster formation over time: Ca 2+ ions can form prenucleation clusters at ambient temperature but show saturation with increasing temperature, whereas Na + and Mg 2+ ions show a rapid increase in cluster size and amount upon increasing time and temperature. A ReaxFF force field has been developed for metal carbonates (CaCO 3 , MgCO 3 and Na 2 CO 3 ) and is used for molecular dynamics simulations to study their behavior in aqueous solution at ambient and supercritical conditions.