A number of DFT programs with various combinations of pseudo-potentials and van der Waals’ dispersive corrections have been used to optimize the structure of sodium peroxodisulfate, Na₂(SO₄)₂, and to calculate the infrared, attenuated total reflectance and terahertz absorption spectra of the powdered crystal. Comparison of the results from the different methods highlights the problems of calculating the absorption spectrum reliably. In particular the low frequency phonon modes are especially sensitive to the choice of grids to represent the wavefunction or the charge distribution, k-point integration grid and the energy cutoff. A comparison is made between the Maxwell-Garnett (MG) and Bruggeman effective medium methods used to account for the effect of crystal shape on the predicted spectrum. Possible scattering of light by air inclusions in the sample and by larger particles of Na₂(SO₄)₂ is also considered using the Mie method. The results of the calculations are compared with experimental measurements of the transmission and attenuated total reflection spectra.

中文翻译：

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探索过二硫酸钠的红外光谱和太赫兹光谱的DFT计算的可靠性

已使用许多具有伪电势和范德华分散度校正的各种组合的DFT程序来优化过氧二硫酸钠Na ₂（SO ₄）_{2的结构。}，并计算粉状晶体的红外光谱，衰减的全反射率和太赫兹吸收光谱。不同方法结果的比较突出了可靠地计算吸收光谱的问题。特别是低频声子模式对表示波函数或电荷分布的网格，k点积分网格和能量截止特别敏感。在Maxwell-Garnett（MG）和Bruggeman有效介质方法之间进行了比较，该方法用于解释晶体形状对预测光谱的影响。样品中的空气夹杂物和较大的Na ₂（SO ₄）₂颗粒可能会散射光也考虑使用三重方法。将计算结果与透射和衰减全反射光谱的实验测量值进行比较。