Nanochemistry Research Institute, Department of Chemistry, Curtin University, Perth, WA, Australia.
Phys Chem Chem Phys. 2011 Oct 6;13(37):16666-79. doi: 10.1039/c1cp21034c. Epub 2011 Aug 18.
A new reactive force field has been derived that allows the modelling of speciation in the aqueous-calcium carbonate system. Using the ReaxFF methodology, which has now been implemented in the program GULP, calcium has been simulated as a fixed charge di-cation species in both crystalline phases, such as calcite and aragonite, as well as in the solution phase. Excluding calcium from the charge equilibration process appears to have no adverse effects for the simulation of species relevant to the aqueous environment. Based on this model, the speciation of carbonic acid, bicarbonate and carbonate have been examined in microsolvated conditions, as well as bulk water. When immersed in a droplet of 98 water molecules and two hydronium ions, the carbonate ion is rapidly converted to bicarbonate, and ultimately carbonic acid, which is formed as the metastable cis-trans isomer under kinetic control. Both first principles and ReaxFF calculations exhibit the same behaviour, but the longer timescale accessible to the latter allows the diffusion of the carbonic acid to the surface of the water to be observed, where it is more stable at the interface. Calcium carbonate is also examined as ion pairs in solution for both CaCO(3)(0)((aq)) and CaHCO(3)(+)((aq)), in addition to the (1014) surface in contact with water.
一种新的反应力场已经被推导出来，允许在碳酸钙水体系中进行形态建模。使用 ReaxFF 方法，该方法现在已经在 GULP 程序中实现，钙被模拟为晶相（如方解石和文石）以及溶液相中固定电荷的二价阳离子。在不进行电荷平衡过程的情况下排除钙，似乎对模拟与水相环境相关的物种没有不利影响。基于该模型，研究了碳酸、碳酸氢根和碳酸根在微溶剂化条件下以及在大体积水中的形态。当浸入 98 个水分子和两个水合氢离子的液滴中时，碳酸根离子迅速转化为碳酸氢根离子，最终在动力学控制下形成不稳定的顺反异构体的碳酸。第一性原理和 ReaxFF 计算都表现出相同的行为，但后者更长的时间尺度允许观察碳酸向水表面的扩散，在界面处它更稳定。碳酸钙也被研究为溶液中的离子对，包括 CaCO(3)(0)((aq))和 CaHCO(3)(+)((aq))，以及与水接触的(1014)表面。
