Demichelis R, Noel Y, Civalleri B, Roetti C, Ferrero M, Dovesi R
Dipartimento di Chimica IFM, Università di Torino, Via P. Giuria 7, 10125 Torino, Italy.
J Phys Chem B. 2007 Aug 9;111(31):9337-46. doi: 10.1021/jp072501d. Epub 2007 Jul 13.
The vibrational spectrum of alpha-AlOOH diaspore has been calculated at the B3LYP level of theory with a double-zeta quality Gaussian-type basis set by using the periodic ab initio CRYSTAL code. Harmonic frequencies at the Gamma point and the corresponding 48 normal modes are analyzed and classified in terms of simple models (octahedra modes, hydrogen stretching, bending, rotations) by direct inspection of eigenvectors, graphical representation, and isotopic substitution. Hydrogen modes are fully separated from the octahedra modes appearing under 800 cm(-1); bending modes are located in the range of 1040-1290 cm(-1), whereas stretching modes appear at 3130-3170 cm(-1). The available experimental IR and Raman spectra are characterized by broad bands, in some cases as large as 800 cm(-1), and individual peaks are obtained by decomposing these bands in terms of Lorentz-Gauss product functions; such a fitting procedure is affected by a relatively large degree of arbitrariness. The comparison of our calculated data with the most complete sets of experimental data shows, nevertheless, a relatively good agreement for all but the H modes; the mean absolute differences for modes not involving H are 10.9 and 7.2 cm(-1) for the IR and the Raman spectra, respectively, the maximum differences being 15.5 and 18.2 cm(-1). For the H bending modes, differences increase to 30 and 37 cm(-1), and for the stretching modes, the calculated frequencies are about 200 cm(-1) higher than the experimental ones; this is not surprising, as anharmonicity is expected to red shift the OH stretching by about 150 cm(-1) in isolated OH groups and even more when the latter is involved in strong hydrogen bonds, as is the case here.
利用周期性从头算CRYSTAL程序，在B3LYP理论水平下，采用双ζ质量的高斯型基组计算了α-AlOOH水铝石的振动光谱。通过直接检查本征向量、图形表示和同位素取代，在Γ点的谐波频率以及相应的48个简正模式按照简单模型（八面体模式、氢伸缩、弯曲、旋转）进行了分析和分类。氢模式与出现在800 cm⁻¹以下的八面体模式完全分离；弯曲模式位于1040 - 1290 cm⁻¹范围内，而伸缩模式出现在3130 - 3170 cm⁻¹处。现有的实验红外光谱和拉曼光谱以宽带为特征，在某些情况下宽带宽度可达800 cm⁻¹，通过用洛伦兹 - 高斯乘积函数分解这些谱带来获得各个峰；这样的拟合过程受到较大程度的任意性影响。然而，将我们的计算数据与最完整的实验数据集进行比较，除了H模式外，其他模式都显示出相对较好的一致性；对于不涉及H的模式，红外光谱和拉曼光谱的平均绝对差值分别为10.9和7.2 cm⁻¹，最大差值分别为15.5和18.2 cm⁻¹。对于H弯曲模式，差值增加到30和37 cm⁻¹，对于伸缩模式，计算频率比实验频率高约200 cm⁻¹；这并不奇怪，因为预计非谐性会使孤立OH基团中的OH伸缩频率红移约150 cm⁻¹，而当后者参与强氢键时，红移会更大，此处就是这种情况。
