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首页> 外文期刊>Crystal growth & design >Assessing the role of water on the electronic structure and vibrational spectra of monohydrated L-aspartic acid crystals
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Assessing the role of water on the electronic structure and vibrational spectra of monohydrated L-aspartic acid crystals

机译：评估水对一水合L-天冬氨酸晶体的电子结构和振动光谱的作用

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摘要

In this work, we compare the calculated electronic and vibrational properties (infrared and Raman spectra) of anhydrous and monohydrated L-aspartic acid crystals to unveil the role of water in the later. This is accomplished through density functional theory (DFT) simulations within the Tkatchenko and Scheffler dispersion corrected generalized gradient approximation (GGA+TS). Both crystals are shown to have indirect band gaps and the simulations predict that water has a small effect on the Kohn-Sham band gap value (60 meV). Δ-sol corrected gaps, in contrast, exhibited a larger difference between the anhydrous and monohydrated crystals (main gap 0.30 eV larger for the latter). The conduction bands of the monohydrated species are much flatter because of structural changes produced by the presence of water, which leads to very large electron effective masses. However, the hole effective mass along the stacking direction of water molecules in the GGA+TS optimized monohydrated crystal is smaller than in other directions, suggesting that water stacking can improve on hole transport in similar bioorganic systems. These effects highlight the complex role of water on the carrier transport properties in monohydrated l-aspartic acid crystals, which is in contrast with the general belief that water simply increases the electrical conductance in molecular crystals. Finally, the calculated infrared and Raman spectra of the monohydrated phase exhibit molecular water vibrational signatures as well as water related peak shifts of as much as 100 cm~（-1） in comparison to those of the anhydrous structure. Remarkable water related Raman intensity peaks were obtained for the monohydrated crystal in the wavenumber ranges between 600 and 1000 cm~ (-1) and between 2350 and 3450 cm~(-1), while for the infrared spectrum, a set of water absorption bands can be clearly identified in the 1550-1750 and 2800-3400 cm~(-1) wavenumber intervals.
机译：在这项工作中，我们比较了无水和一水合L-天门冬氨酸晶体的计算电子和振动特性（红外和拉曼光谱），以揭示水在后面的作用。这是通过Tkatchenko和Scheffler色散校正广义梯度逼近（GGA + TS）中的密度泛函理论（DFT）模拟来完成的。两种晶体均显示具有间接带隙，并且模拟预测水对Kohn-Sham带隙值（60 meV）的影响很小。相反，经Δ-sol校正的间隙在无水和一水合晶体之间表现出较大的差异（主间隙对后者而言大0.30 eV）。一水合物种的导带要平坦得多，因为水的存在会引起结构变化，从而导致很大的电子有效质量。然而，在GGA + TS优化的一水合晶体中，沿着水分子堆积方向的空穴有效质量要比其他方向小，这表明在类似的生物有机系统中，水的堆积可以改善空穴传输。这些效应突出了水对一水合1-天冬氨酸晶体中载流子传输特性的复杂作用，这与普遍认为水仅增加分子晶体中的电导率的一般看法相反。最后，与无水结构相比，一水合相的红外光谱和拉曼光谱表现出分子水振动特征以及与水有关的峰位移高达100 cm〜（-1）。在600至1000 cm〜（-1）和2350至3450 cm〜（-1）的波数范围内，一水合晶体获得了明显的与水有关的拉曼强度峰，而对于红外光谱，则获得了一组吸水带可以在1550-1750和2800-3400 cm〜（-1）的波数间隔中清楚地识别出。

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