Anomalous Temperature Dependence of the Lowest-Frequency Lattice Vibration in Crystalline γ-Aminobutyric Acid
Anomalous Temperature Dependence of the Lowest-Frequency Lattice Vibration in Crystalline γ-Aminobutyric Acid
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DOI：
10.1021/acs.jpca.8b12572
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发表时间：
2019-03-14
影响因子：
2.9
通讯作者：
Korter, Timothy M.
中科院分区：
文献类型：
--
作者：
Dampf, Sara J.;Korter, Timothy M.
结晶γ-氨基丁酸 (GABA) 在低频晶格振动中表现出不寻常的热行为，在 290 K 时发生在 37.2 cm(-1) 处，但当样品冷却至 78 K 时，热行为急剧下降 34.0%。分子晶体中的晶格振动是分子间力特征的指标，这种振动的非凡温度敏感性为了解固体内的局部环境提供了新的见解。 GABA 晶体的固态密度泛函理论模拟发现，这种反常频移是基于大致相同的分子间氢键强度的意外差异。这是通过绘制控制 GABA 固体太赫兹频率运动的势能表面并使用准调和近似来模拟所有晶格振动对温度引起的晶胞体积变化的响应来实现的，这些变化是通过分子间相互作用的非调和特性引起的。分析表明，所讨论的振动本质上是旋转的，并且涉及晶体中特定的弱分子间 N-H 中心点中心点中心点中心点 O 氢键的显着变形，从而导致其独特的热响应。
Crystalline gamma-aminobutyric acid (GABA) exhibits unusual thermal behavior in a low-frequency lattice vibration that occurs at 37.2 cm(-1) at 290 K but decreases dramatically by 34.0% when the sample is cooled to 78 K. Lattice vibrations in molecular crystals are indicators of intermolecular force characteristics, and the extraordinary temperature sensitivity of this vibration offers new insight into the local environment within the solid. Solid-state density functional theory simulations of the GABA crystal have found this anomalous frequency shift is based in unexpected differences in the strengths of the intermolecular hydrogen bonds that are cursorily the same. This was accomplished through mapping of the potential energy surfaces governing the terahertz-frequency motions of the GABA solid and use of the quasiharmonic approximation to model the response of all the lattice vibrations to temperature-induced unit cell volume changes brought about through the anharmonic character of the intermolecular interactions. The analysis reveals that the vibration in question is rotational in nature and involves the significant distortion of a specific weak intermolecular N-H center dot center dot center dot O hydrogen bond in the crystal that results in its unique thermal response.