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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >DFT Calculations with van der Waals Interactions of Hydrated Calcium Carbonate Crystals CaCO3 center dot(H2O, 6H(2)O): Structural, Electronic, Optical, and Vibrational Properties
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DFT Calculations with van der Waals Interactions of Hydrated Calcium Carbonate Crystals CaCO3 center dot(H2O, 6H(2)O): Structural, Electronic, Optical, and Vibrational Properties

机译：水合碳酸钙晶体CaCO3中心点（H2O，6H（2）O）与范德华相互作用的DFT计算：结构，电子，光学和振动特性

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摘要

The role of hydration on the structural, electronic, optical, and vibrational properties of monohydrated (CaCO3 center dot H2O, hexagonal, P3(1), Z = 9) and hexahydrated (CaCO3 center dot 6H(2)O, monoclinic, C2/c, Z = 4) calcite crystals is assessed with the help of published experimental and theoretical data applying density functional theory within the generalized gradient approximation and a dispersion correction scheme. We show that the presence of water increases the main band gap of monohydrocalcite by 0.4 eV relative to the anhydrous structure, although practically not changing the hexahydrocalcite band gap. The gap type, however, is modified from indirect to direct as one switches from the monohydrated to the hexahydrated crystal. A good agreement was obtained between the simulated vibrational infrared and Raman spectra and the experimental data, with an infrared signature of hexahydrocalcite relative to monohydrocalcite being observed at 837 cm(-1). Other important vibrational signatures of the lattice, water molecules, and CO32- were identified as well. Analysis of the phonon dispersion curves shows that, as the hydration level of calcite increases, the longitudinal optical transverse optical phonon splitting becomes smaller. The thermodynamics properties of hexahydrocalcite as a function of temperature resemble closely those of calcite, while monohydrocalcite exhibits a very distinct behavior.
机译：水合作用对一水合物（CaCO3中心点H2O，六角形，P3（1），Z = 9）和六水合物（CaCO3中心点6H（2）O，单斜晶，C2 /）的结构，电子，光学和振动性质的作用c，Z = 4）方解石晶体是借助已发布的实验和理论数据，在广义梯度近似和色散校正方案内应用密度泛函理论进行评估的。我们表明，水的存在使单氢方解石的主带隙相对于无水结构增加了0.4 eV，尽管实际上并没有改变六氢方解石的带隙。然而，随着从一水合晶体到六水合晶体的转换，间隙类型从间接改变为直接。在模拟振动红外光谱和拉曼光谱与实验数据之间获得了良好的一致性，在837 cm（-1）处观察到六氢方解石相对于单氢方解石的红外特征。还确定了晶格，水分子和CO32-的其他重要振动特征。对声子色散曲线的分析表明，随着方解石水合度的增加，纵向光学横向光学声子分裂变小。六氢方解石的热力学性质随温度的变化与方解石极为相似，而单氢方解石表现出非常不同的行为。

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