Reactive force fields for aqueous and interfacial magnesium carbonate formation
Reactive force fields for aqueous and interfacial magnesium carbonate formation
复制标题
水相和界面碳酸镁形成的反作用力场
DOI：
10.1039/d1cp02627e
复制
发表时间：
2021
影响因子：
3.3
通讯作者：
Qomi, Mohammad Javad
中科院分区：
文献类型：
--
作者：
Zare, Siavash;Qomi, Mohammad Javad
我们开发了适用于两种环境的Mg/C/O/H ReaxFF参数集：溶液中镁离子的水力场和矿物及矿物-水界面的界面力场。由于镁是高度离子的，我们选择固定镁电荷，并通过库仑、Lennard-Jones和Buckingham势模拟其与C/O/H的相互作用。我们对几种晶体结构，包括水镁石、镁砂、氧化镁、氢化镁和碳化镁，以及水相力场中的镁离子水结合能，对力场进行了参数化。然后，我们对其他含镁晶体、溶剂分离和接触离子对以及单分子/多层水在矿物表面的吸附能进行了测试。我们还将力场应用于镁橄榄石-水和水镁石-水界面，其中含有碳酸氢根离子。我们观察到，长程质子转移机制使重碳酸盐离子在界面上去质子化为碳酸盐。自由能计算表明，碳酸盐可以以约0.22 eV的势垒附着在镁表面，这与镁-碳酸盐水溶液离子配对所需的自由能一致。此外，氢氧离子在镁橄榄岩表面形成的水层中的扩散常数具有各向异性和非均质性。这些发现有助于解释实验中观察到的菱镁矿在缺水条件下在矿物-水-二氧化碳界面上的低温快速成核和生长。
We develop Mg/C/O/H ReaxFF parameter sets for two environments: an aqueous force field for magnesium ions in solution and an interfacial force field for minerals and mineral–water interfaces. Since magnesium is highly ionic, we choose to fix the magnesium charge and model its interaction with C/O/H through Coulomb, Lennard-Jones, and Buckingham potentials. We parameterize the forcefields against several crystal structures, including brucite, magnesite, magnesia, magnesium hydride, and magnesium carbide, as well as Mg2+ water binding energies for the aqueous forcefield. Then, we test the forcefield for other magnesium-containing crystals, solvent separated and contact ion-pairs and single-molecule/multilayer water adsorption energies on mineral surfaces. We also apply the forcefield to the forsterite–water and brucite–water interface that contains a bicarbonate ion. We observe that a long-range proton transfer mechanism deprotonates the bicarbonate ion to carbonate at the interface. Free energy calculations show that carbonate can attach to the magnesium surface with an energy barrier of about 0.22 eV, consistent with the free energy required for aqueous Mg–CO3 ion pairing. Also, the diffusion constant of the hydroxide ions in the water layers formed on the forsterite surface are shown to be anisotropic and heterogeneous. These findings can help explain the experimentally observed fast nucleation and growth of magnesite at low temperature at the mineral–water–CO2 interface in water-poor conditions.