Vibrational mode frequencies of silica species in SiO2-H2O liquids and glasses from ab initio molecular dynamics.
Vibrational mode frequencies of silica species in SiO2-H2O liquids and glasses from ab initio molecular dynamics.
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DOI：
10.1063/1.3703667
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发表时间：
2012-04
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影响因子：
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通讯作者：
G. Spiekermann;M. Steele‐MacInnis;C. Schmidt;S. Jahn
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文献类型：
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作者：
G. Spiekermann;M. Steele‐MacInnis;C. Schmidt;S. Jahn
振动光谱技术通常用于探测水溶液和含水二氧化硅玻璃中二氧化硅物种的原子尺度结构。然而，明确的分配个别光谱特征的特定振动模式是具有挑战性的。在这方面的贡献，我们建立了实验观察到的振动带和从头算分子动力学（MD）的二氧化硅物种在溶液中和含水二氧化硅玻璃之间的连接。使用模式投影方法，我们将二氧化硅物种的振动分解为由几个基本结构亚基产生的子光谱：对称性T（d）的SiO（4）四面体，对称性C（2 v）的桥氧（BO）Si-O-Si，对称性C（2 v）的孪氧O-Si-O，个别Si-OH伸缩，以及H（6）Si（2）O（7）二聚体的特殊的类乙烷对称伸缩贡献。这使我们能够研究这些亚基在任何聚合度下的相关振动，从Q（0）单体到完全聚合的Q（4）四面体。证明这种方法的潜力，补充解释实验光谱，我们比较计算的频率从实验中提取的含水二氧化硅玻璃和二氧化硅物种在水溶液中的拉曼光谱。我们讨论了所观察到的特征，如Q（2）四面体对称伸缩的双峰贡献，单个Si-OH伸缩振动，实验观察到的970 cm（-1）处的带的起源和H（6）Si（2）O（7）二聚体在870 cm（-1）处的乙烷样振动贡献。
Vibrational spectroscopy techniques are commonly used to probe the atomic-scale structure of silica species in aqueous solution and hydrous silica glasses. However, unequivocal assignment of individual spectroscopic features to specific vibrational modes is challenging. In this contribution, we establish a connection between experimentally observed vibrational bands and ab initio molecular dynamics (MD) of silica species in solution and in hydrous silica glass. Using the mode-projection approach, we decompose the vibrations of silica species into subspectra resulting from several fundamental structural subunits: The SiO(4) tetrahedron of symmetry T(d), the bridging oxygen (BO) Si-O-Si of symmetry C(2v), the geminal oxygen O-Si-O of symmetry C(2v), the individual Si-OH stretching, and the specific ethane-like symmetric stretching contribution of the H(6)Si(2)O(7) dimer. This allows us to study relevant vibrations of these subunits in any degree of polymerization, from the Q(0) monomer up to the fully polymerized Q(4) tetrahedra. Demonstrating the potential of this approach for supplementing the interpretation of experimental spectra, we compare the calculated frequencies to those extracted from experimental Raman spectra of hydrous silica glasses and silica species in aqueous solution. We discuss observed features such as the double-peaked contribution of the Q(2) tetrahedral symmetric stretch, the individual Si-OH stretching vibrations, the origin of the experimentally observed band at 970 cm(-1) and the ethane-like vibrational contribution of the H(6)Si(2)O(7) dimer at 870 cm(-1).