School of Earth Sciences, The Ohio State University, 125 South Oval Mall, Columbus, Ohio 43210, USA.
School of Chemistry and Chemical Engineering, Southwest Petroleum University, 8 Xindu Ave., Chengdu 610500, People's Republic of China.
J Chem Phys. 2019 Jan 28;150(4):044703. doi: 10.1063/1.5058770.
Dopants have the potential to locally modify water-olivine interactions, which can impact geological processes, such as weathering, CO sequestration, and abiotic hydrocarbon generation. As a first step in understanding the role of dopants on the water structure and chemistry at water-olivine interfaces, water monomer adsorption on alkaline earth (AE) and transition metal (TM) doped forsterite(010) [MgSiO(010)] surfaces was studied using density functional theory (DFT). Dopants that occur in olivine minerals were considered and consisted of Ca, Sr, and Ba for the AE dopants and Cr, Mn, Fe, Co, and Ni for the TM dopants. The water molecule adsorbs on the olivine surface through a metal-water bond (Me-Ow) and a hydrogen bond with an adjacent surface lattice oxygen (Ox-Hw). A frontier orbital analysis reveals that the 1b, 3a, and 1b (HOMO) of the water molecule are involved in the bonding. All of the TM dopants show strong net Me-Ow covalent bonding between 3a and 1b water orbitals and TM d states, while the AE dopants except for MgSiO(010) show negligible Me-Ow covalent bonding. Both the AE and TM dopants show similar hydrogen bonding features involving both the 1b and 3a orbitals. While the AE cations show an overall lower Me-Ow covalent interaction, the AE dopants have strong electrostatic interactions between the positive metal cation and the negatively charged water dipole. A bonding model incorporating a linear combination of the covalent Me-Ow bond, the Ox-Hw hydrogen bond, the electrostatic interaction between the dopant cation and the HO molecule, and the surface distortion energy is needed to capture the variation in the DFT adsorption energies on the olivine surfaces. The bonding analysis is able to identify the dominant contributions to water-dopant interactions and can serve as a basis for future studies of more realistic water-olivine interfaces.
掺杂剂有可能局部改变水-橄榄石的相互作用，从而影响风化、CO 封存和非生物烃生成等地质过程。为了了解掺杂剂对水-橄榄石界面上水结构和化学性质的影响，我们采用密度泛函理论（DFT）研究了碱性土（AE）和过渡金属（TM）掺杂镁橄榄石（010）[MgSiO（010）]表面上水单体的吸附作用。考虑到橄榄石矿物中存在的掺杂剂，我们选择了 Ca、Sr 和 Ba 作为 AE 掺杂剂，Cr、Mn、Fe、Co 和 Ni 作为 TM 掺杂剂。水分子通过金属-水键（Me-Ow）和与相邻表面晶格氧（Ox-Hw）的氢键吸附在橄榄石表面上。前沿轨道分析表明，水分子的 1b、3a 和 1b（HOMO）轨道参与了成键。所有 TM 掺杂剂都显示出 3a 和 1b 水轨道与 TM d 态之间强烈的净 Me-Ow 共价键，而除了 MgSiO（010）之外的 AE 掺杂剂几乎没有 Me-Ow 共价键。AE 和 TM 掺杂剂都显示出相似的氢键特征，涉及 1b 和 3a 轨道。尽管 AE 阳离子显示出整体较低的 Me-Ow 共价相互作用，但 AE 掺杂剂具有带正电荷的金属阳离子与带负电荷的水分子偶极子之间的强静电相互作用。为了捕捉橄榄石表面上 DFT 吸附能的变化，需要一种结合共价 Me-Ow 键、Ox-Hw 氢键、掺杂剂阳离子与 HO 分子之间的静电相互作用以及表面畸变能的线性组合的成键模型。成键分析能够确定水-掺杂剂相互作用的主要贡献，并为未来更真实的水-橄榄石界面的研究提供基础。
