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首页> 外文期刊>Journal of Non-Crystalline Solids: A Journal Devoted to Oxide, Halide, Chalcogenide and Metallic Glasses, Amorphous Semiconductors, Non-Crystalline Films, Glass-Ceramics and Glassy Composites >Calculation of the electric field gradients at 'tricluster'-like O atoms in the polymorphs of Al2SiO5 and in aluminosilicate molecules: models for tricluster O atoms in glasses
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Calculation of the electric field gradients at 'tricluster'-like O atoms in the polymorphs of Al2SiO5 and in aluminosilicate molecules: models for tricluster O atoms in glasses

机译：Al2SiO5多晶型物和硅铝酸盐分子中“类似三聚体”的O原子处的电场梯度的计算：玻璃中三聚体O原子的模型

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O-17 NMR studies and molecular dynamics calculations have suggested the presence in some aluminosilicate glasses of 'tricluster' O atoms, O[3], O atoms which are bonded to three four-coordinated Al or Si atoms. Recent ab initio molecular orbital calculations on simple models for such species obtained electric field gradients (EFG) and nuclear quadrupole coupling constants (NQCC) at these O atoms which were considerably larger than those observed by NMR, casting doubt on the assignment of such features to triclusters. We present calculations using density functional theory (DFT) and full-potential linearized augmented plane wave (FLAPW) method on the O EFG values for the eight chemically inequivalent O sites in the andalusite and sillimanite polymorphs of Al2SiO5, most of which have local geometries closely related to triclusters. We also present calculated O EFG values for several different tricluster model species using Hartree-Fock and DFT methods within a cluster approach. These new model species contain tricluster O atoms with either non-planar geometries about O or O-O edge-sharing geometries. The edge-sharing tricluster geometries give O EFG values which are systematically much lower than those of the species previously considered, Many well-characterized examples of such compounds have been reported in the inorganic chemistry literature. Some of the edge-sharing clusters give O EFG values and NMR shieldings in the range attributed to tricluster O atoms in Ca aluminosilicate glasses. O EFG values calculated by both band and cluster methods for tricluster O atoms are found to correlate well with the sum of the Pauling or Brown bond strength at the O, weighted by the fractional covalency of the bond. For the more interesting edge-sharing species this EFG vs. (bond strength x covalency) correlation line is offset from that for the corner-sharing geometries by about 0.5 a.u., corresponding roughly to a systematic reduction of 2.5 MHz in the coupling constant. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 50]
机译：O-17 NMR研究和分子动力学计算表明，在某些硅铝酸盐玻璃中存在与3个四配位的Al或Si原子键合的'三聚体'O原子，O [3]，O原子。最近在这类物质的简单模型上从头算起的分子轨道计算获得了在这些O原子处的电场梯度（EFG）和核四极偶合常数（NQCC），其比通过NMR观察到的大得多，这使人们对这些特征的归属产生了疑问。三角帆。我们介绍了使用密度泛函理论（DFT）和全能线性化增强平面波（FLAPW）方法对Al2SiO5的红柱石和硅线石多晶型物中8个化学等价O位点的O EFG值进行计算的方法与短柄短毛有关。我们还介绍了在群集方法中使用Hartree-Fock和DFT方法为几种不同的三角洲模型物种计算的O EFG值。这些新的模型物种包含具有约O或O-O边共享几何形状的非平面几何形状的三聚体O原子。边缘共享的三角形几何形状给出的O EFG值系统地比先前考虑的物种低得多。无机化学文献中已报道了这类化合物的许多充分表征的实例。一些边缘共享簇给出的O EFG值和NMR屏蔽范围归因于Ca铝硅酸盐玻璃中的三聚体O原子。发现通过带和簇方法为三聚体O原子计算的O EFG值与在O处的鲍林或布朗键强度之和很好地相关，并通过键的分数共价加权。对于更有趣的边缘共享种类，此EFG与（粘合强度x共价）相关线相对于角共享几何形状的相关线偏移了约0.5 a.u.，大致相当于系统地将耦合常数减小了2.5 MHz。 （C）2001 Elsevier Science B.V.保留所有权利。 [参考：50]

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