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首页> 外文期刊>Journal of Computer Chemistry, Japan -International Edition >Revisiting the Nature of Si-O-Si Bridging
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Revisiting the Nature of Si-O-Si Bridging

机译：重访Si-O-Si桥接的本质

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Non-empirical calculation based on the Schr?dinger equation is an appropriate tool for investigating the relationship among Si-O-Si angle, Si-O bond length, Si-O bond strength, and electronic structure. However, past studies could not reach a consensus about the equilibrium structure of the C_(2v) pyrosilisic acid molecule. Moreover, the structure of disiloxane, the simplest siloxane molecule, could not be reproduced using non-empirical molecular orbital calculations. In this study, I checked the reproducibility of various model chemistries and basis sets, and found that employing the post-Hartree-Fock method and a larger basis set (at least, aug-cc-pVTZ) is necessary for accurate calculation of the disiloxane molecule. In contrast to past studies on molecular orbitals, the present study reveals no significant occupancy in the Si 3d orbitals. The total energy landscape of the C_(2v) pyrosilisic acid molecule is calculated by using the coupled cluster method concerning three excited electrons and the aug-cc-pVTZ basis set. The stable bond length for Si-O_(br) is 1.604 ?, and the stable Si-O-Si angle is 159.449°. There are gentle curves around the stable angles for each bond length comparing with bond length direction. The stable angle for each bond length decreased with increasing Si-O_(br) bond length. The weakening of the Si-O_(br) bond with decreasing Si-O-Si bond angle can be explained by the decrease in the bond index and the increase in the orbital energy for Si-O_(br) σ-bond. Consequently, hybridization of the valence electrons of the bridging oxygen with decreasing Si-O-Si angle weakens the Si-O_(br) σ-bond. Electrostatic potential favors a straight configuration because of the repulsion between the SiO_(4) tetrahedra, while the valence electrons of the bridging oxygen favor a bent configuration. These two competing behaviors can explain the bent configuration of pyrosilisic acid without considering d-p π bonding.
机译：基于Schr？dinger方程的非经验计算是研究Si-O-Si角，Si-O键长，Si-O键强度和电子结构之间关系的合适工具。但是，以往的研究未能就C_（2v）焦硅酸分子的平衡结构达成共识。此外，使用非经验分子轨道计算无法复制最简单的硅氧烷分子二硅氧烷的结构。在这项研究中，我检查了各种化学模型和基集的可重复性，发现使用后Hartree-Fock方法和更大的基集（至少是aug-cc-pVTZ）对于精确计算二硅氧烷是必要的分子。与过去对分子轨道的研究相比，本研究表明在Si 3d轨道中没有显着的占据。通过使用涉及三个受激电子的耦合簇方法和aug-cc-pVTZ基集，计算C_（2v）焦硅酸分子的总能态。 Si-O_（br）的稳定键长为1.604Ω，稳定的Si-O-Si角为159.449°。与粘结长度方向相比，每种粘结长度在稳定角度周围都有平缓的曲线。每个键长的稳定角随Si-O_（br）键长的增加而减小。随着Si-O-Si键角的减小，Si-O_（br）键的弱化可以通过Si-O_（br）σ键的键合指数的降低和轨道能量的增加来解释。因此，桥接氧的价电子与减小的Si-O-Si角的杂化削弱了Si-O_（br）σ键。由于SiO_（4）四面体之间的排斥，静电势有利于笔直构型，而桥接氧的价电子则有利于弯曲构型。这两种竞争行为可以解释焦硅酸的弯曲构型，而无需考虑d-pπ键。

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