A Quantum Mechanically Derived Force Field To Predict CO₂ Adsorption on Calcite {10.4} in an Aqueous Environment

Abstract

Density functional theory (DFT) with semiempirical dispersion corrections (DFT-D2) has been used to calculate the binding energy of a CO2 molecule on the calcite {10.4} surface for different positions and orientations. This generated potential energy landscape was then used to parametrize a classical force field. From this, we used metadynamics (MTD) to derive free energy profiles at 300 and 350 K for CO2 binding to calcite, CO2 binding with Ca2+, and pairing of two CO2 molecules, all for aqueous conditions. We subsequently performed classical molecular dynamics (MD) simulations of CO2 and water on the {10.4} surface at pressures and temperatures relevant for CO2 geological storage. Density profiles show characteristic structured water layering at the calcite surface and two distinct phases of water and CO2. We have also calculated the densities of the CO2-rich and water-rich phases and thereby determined the mutual solubilities. For all the pressures and temperatures in the studied range, CO2 was unable to penetrate the ordered water layers and adsorb directly on the solid surface. This is further confirmed by the free energy profiles showing that in the presence of water there is neither direct adsorption to the {10.4} surface nor contact binding of CO2 with Ca2+. Rather, we saw a weak affinity for the surface of the ordered water layers. At 5 MPa and 323 K, we observed the nucleation of a CO2 droplet located above two structured water layers over the solid. It could not penetrate the structured water but remained bound to the second water layer for the first 10 ns of the simulation before eventually detaching and diffusing away.

Wetting Properties of the CO2–Water–Calcite System via Molecular Simulations: Shape and Size Effects

“…This suggests interaction between the mineral surface and CO 2 . We observed a similar but weaker interaction between CO 2 and the {10.4} surface of calcite in our previous simulations 24 where bulk water formed 3 structured layers above the surface, excluding CO 2 from direct interaction with the mineral. In the present study, the calcite slab was not completely hydrated and CO 2 was able to bind more strongly to the surface and the first hydration layer.…”

“…One of the main reasons why calcite has been ignored in modelling studies so far is most likely the lack of reliable force field parameters for its interaction with CO 2 . The purpose of this study was to use our new set of force field parameters 24 to predict the contact angles in the CO 2 -water IFT and CO 2 -water-calcite systems. We have conducted a comparative investigation by simulating spherical droplets and cylindrical filaments of equivalent size to show the results of using different configurations and to verify at which length scales, size effects on the contact angle become negligible.…”

Wetting Properties of the CO2–Water–Calcite System via Molecular Simulations: Shape and Size Effects

“…The interactions between CO 2 and calcite were described by our new set of force field parameters. 24 For van der Waals CO 2 -CO 2 , water-water and CO 2 -water interactions, we used a cutoff distance of 10 Å, whereas for the dispersion interactions of calcite with both CO 2 and water, we used the tapering function of Mei et al; 65…”

Predicting hydration layers on surfaces using deep learning

“…12 Alongside this, a wealth of computational studies of the calcite-water interface have been undertaken, providing a critical background of structural understanding and reliable forces elds necessary for our approach. These studies extensively delineate the calcite (1014) surface and water interactions, 26,27 AFM imaging, 16,[28][29][30][31] surface ion dissolution, 32,33 and effects of point defects and step edges on the hydration layer densities. 14,[34][35][36][37] Alongside calcite, we further consider the other most common polymorphs of CaCO 3 , aragonite and vaterite.…”