Benoit Magali, Profeta Mickaël, Mauri Francesco, Pickard Chris J, Tuckerman Mark E
CEMES, 29 rue Jeanne Marvig, BP 94347, 31055 Toulouse Cedex 4, France.
J Phys Chem B. 2005 Apr 7;109(13):6052-60. doi: 10.1021/jp0492570.
We have computed the (17)O NMR parameters of an amorphous calcium aluminosilicate (CAS) from first-principles. The atomic coordinates of a CAS glass of composition (CaO)(0.21)(Al(2)O (3))(0.12)(SiO (2))(0.67) were obtained by quenching a liquid to room temperature by the means of ab initio molecular-dynamics simulations of the Car-Parrinello type. The structure of the glass is found to be overall in good agreement with diffraction experiments. Some excess nonbridging O (NBO) atoms are found and are compensated by tricluster O atoms, i.e., by 3-fold coordinated O atoms to 4-fold coordinated Al or Si atoms. The glass coordinates were used to compute the (17)O NMR parameters using GGA-DFT and a correction of the Ca 3d orbital energy. The chemical shifts and the electric field gradients were obtained with the gauge including projector augmented-wave (GIPAW) and the projector augmented-wave (PAW) methods, respectively. The simulated 2D-3QMAS NMR spectrum of the CAS glass is in very good agreement with the available experimental data, notably because it takes into account the disorder present in the glass. This agreement further validates our CAS glass model. We show that the oxygen triclusters are not visible in a 2D-3QMAS NMR (17)O spectrum since their NMR parameters overlap with those of the Al-O-Si, Si-O-Si, or Al-O-Al sites. Finally, correlations between the structural characteristics and the values of the NMR parameters are extracted from the calculation with the aim of helping the interpretation of NMR spectra of glasses of similar compositions.
我们通过第一性原理计算了非晶态钙铝硅酸盐（CAS）的(17)O核磁共振参数。通过Car-Parrinello型从头算分子动力学模拟将液体淬火至室温，得到了组成为(CaO)(0.21)(Al₂O₃)(0.12)(SiO₂)(0.67)的CAS玻璃的原子坐标。发现该玻璃的结构总体上与衍射实验结果吻合良好。发现了一些多余的非桥氧（NBO）原子，并由三簇氧原子补偿，即由与4配位的Al或Si原子形成3配位的氧原子。利用广义梯度近似密度泛函理论（GGA-DFT）和Ca 3d轨道能量校正，使用玻璃坐标计算(17)O核磁共振参数。分别采用含投影增强波的规范（GIPAW）方法和投影增强波（PAW）方法获得化学位移和电场梯度。CAS玻璃的模拟二维三量子魔角旋转核磁共振谱与现有实验数据非常吻合，特别是因为它考虑了玻璃中存在的无序性。这种吻合进一步验证了我们的CAS玻璃模型。我们表明，氧三簇在二维三量子魔角旋转核磁共振(17)O谱中不可见，因为它们的核磁共振参数与Al-O-Si、Si-O-Si或Al-O-Al位点的参数重叠。最后，从计算中提取结构特征与核磁共振参数值之间的相关性，以帮助解释类似组成玻璃的核磁共振谱。
