Calcium silicates are the most predominant phases in ordinary Portland cement, inside which magnesium is one of the momentous impurities. In this work, using the first-principles density functional theory (DFT), the impurity formation energy (E_for) of Mg substituting Ca was calculated. The adsorption energy (E_ad) and configuration of the single water molecule over Mg-doped β-dicalcium silicate (β-C₂S) and M3-tricalcium silicate (M3-C₃S) surfaces were investigated. The obtained Mg-doped results were compared with the pristine results to reveal the impact of Mg doping. The results show that the E_for was positive for all but one of the calcium silicates surfaces (ranged from –0.02 eV to 1.58 eV), indicating the Mg substituting for Ca was not energetically favorable. The E_ad of a water molecule on Mg-doped β-C₂S surfaces ranged from –0.598 eV to −1.249 eV with the molecular adsorption being the energetically favorable form. In contrast, the E_ad on M3-C₃S surfaces ranged from −0.699 eV to −4.008 eV and the more energetically favorable adsorption on M3-C₃S surfaces was dissociative adsorption. The influence of Mg doping was important since it affected the reactivity of surface Ca/Mg sites, the E_ad of the single water adsorption, as well as the adsorption configuration compared with the water adsorption on pristine surfaces.

中文翻译：

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镁杂质在硅酸钙低指数表面水吸附中的作用：DFT-D研究

硅酸钙是普通波特兰水泥中最主要的相，其中镁是重要的杂质之一。在这项工作中，使用第一原理密度泛函理论（DFT），计算了取代Ca的Mg的杂质形成能（E _for）。吸附能（Ë_广告）和单一水分子上的Mg掺杂β-硅酸二钙（β-C的配置₂ S）和M3-硅酸三钙（M3-C ₃ S）的表面进行了研究。将获得的镁掺杂结果与原始结果进行比较，以揭示镁掺杂的影响。结果表明，该Ë_为除一个硅酸钙表面（范围从–0.02 eV到1.58 eV）外，所有表面均为正值，表明用Mg代替Ca在能量上不利。对E_广告水分子对掺杂Mg的β-C ₂小号表面从-0.598 eV的范围到-1.249 eV的与所述分子吸附是所述能量上有利的形式。相反，在M3-C ₃ S表面上的E _ad在-0.699eV至-4.008eV的范围内，并且在M3-C ₃ S表面上在能量上更有利的吸附是解离吸附。镁掺杂的影响很重要，因为它影响表面Ca / Mg位置，E _ad的反应性。 单一水的吸附量以及与原始表面上的水吸附相比的吸附构型。