The Calcite (104) Surface - Electrolyte Structure: A 3D Comparison of Surface X-Ray Diffraction and Simulations

Abstract

<div>Adsorption and incorporation of ions is known to influence the morphology and growth of calcite. Using surface X-ray diffraction, the interfacial structure of calcite in contact with CaCO3, MgCl2, CaCl2</div><div>and BaCl2 solutions was determined. All of these conditions yield a comparable interfacial structure,</div><div>meaning that there is no significant ion adsorption. This allows for the first time a thorough comparison in all three dimensions with state-of-the-art computer simulations, involving molecular dynamics</div><div>based on both DFT and two different force field models. Additionally, the simulated structures are</div><div>used to calculate the corresponding structure factors, which in turn are compared to those obtained</div><div>from experiment, thereby avoiding the need for fitting or subjective interpretation. In general, there</div><div>is a good agreement between experiment and the simulations, though there are some small discrepancies in the atomic positions, which lead to an inadequate fit of certain features characteristic of the</div><div>structure of water at the interface. Of the three simulation methods examined, the DFT results were</div><div>found to agree best with the experimental structure.</div>

Determining the Complete Stability of Calcite Kink Sites: Real vs Ideal

“…Similarly, the calcite (1 0 1 4)-water interface is also known to have at least two well-defined ordered water layers with a strong orientational preference that maximizes the interaction of molecules with the exposed ions in the underlying surface. 11,12,14 Hence, there is a strong physical justification for the presence of such a large interfacial potential at the calcite-water interface.…”

“…This is because the rhombohedral calcite structure gives rise to stable (1 0 1 4) surfaces that often dominate the observed morphology of macroscopically large crystals. Such extended terraces of predominantly clean surfaces have allowed the study of the structure of the calcite-water interface via X-ray reflectivity 11,12 and high resolution atomic force microscopy, 13,14 while the latter also provides considerable information about the dissolution and growth at steps. 15 The (1 0 1 4) surface of calcite can exhibit two kinds of step along the ⟨4 4 1⟩ or ⟨4 8 1⟩ directions at islands or etch pits, named acute and obtuse, which reflect the angles (78 • and 102 • , respectively) that the cleaved structure makes with the terrace at the step.…”