Incorporation of Mg2+ in surface Ca2+ sites of aragonite: an ab initio study
Incorporation of Mg2+ in surface Ca2+ sites of aragonite: an ab initio study
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DOI：
10.1186/s40645-015-0039-4
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发表时间：
2015-04-02
影响因子：
3.9
通讯作者：
Nagai, Takaya
中科院分区：
文献类型：
--
作者：
Kawano, Jun;Sakuma, Hiroshi;Nagai, Takaya
含Mg2+文石表面的第一性原理计算是重要的，因为Mg2+可以影响碳酸钙多晶的生长。在文石{001}和{110}表面结合Mg2+取代Ca2+的新计算阐明了Mg2+在文石表面附近的稳定性和含有Mg2+的文石表面的结构。结果表明，Mg2+在表面位置对Ca2+的取代能比在体结构中低，并且Mg2+可以很容易地结合到表面位置；然而，当Mg2+取代Ca2+的位置比第二Ca2+层更深时，取代能接近体结构的值。此外，文石表面的Mg2+对表面结构有显著影响。特别是，当Mg2+在{001}表面的顶层甚至在{110}表面的深层取代Ca2+时，CO3基团旋转以实现六坐标几何。旋转可以使Mg2+周围的原子结构松弛，降低取代能。本研究中观察到的Mg2+诱导文石表面的结构重排可能改变了文石的稳定性，并影响了CaCO3的多晶选择。
First-principles calculations of Mg2+-containing aragonite surfaces are important because Mg2+ can affect the growth of calcium carbonate polymorphs. New calculations that incorporate Mg2+ substitution for Ca2+ in the aragonite {001} and {110} surfaces clarify the stability of Mg2+ near the aragonite surface and the structure of the Mg2+-containing aragonite surface. The results suggest that the Mg2+ substitution energy for Ca2+ at surface sites is lower than that in the bulk structure and that Mg2+ can be easily incorporated into the surface sites; however, when Mg2+ is substituted for Ca2+ in sites deeper than the second Ca2+ layer, the substitution energy approaches the value of the bulk structure. Furthermore, Mg2+ at the aragonite surface has a significant effect on the surface structure. In particular, CO3 groups rotate to achieve six-coordinate geometry when Mg2+ is substituted for Ca2+ in the top layer of the {001} surface or even in the deeper layers of the {110} surface. The rotation may relax the atomic structure around Mg2+ and reduces the substitution energy. The structural rearrangements observed in this study of the aragonite surface induced by Mg2+ likely change the stability of aragonite and affect the polymorph selection of CaCO3.