Temperature-Dependent Terahertz Spectra of Isonicotinamide in the Form I Studied Using the Quasi-Harmonic Approximation |
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| Authors: | Yin Li Prof Dr Yiwen Sun Qiqi Li Jiangtao Lei Bo Yang Yun Shen Yingxiang Cai Prof Dr Xiaohua Deng |
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| Institution: | 1. Department of Physics, School of Physics and Materials Science, Nanchang University, Xuefu Avenue 999, Nanchang City, 330031 China;2. Health Science Center, School of Biomedical Engineering, Shenzhen University, Shenzhen City, 518060 China;3. Institute of Space Science and Technology, Nanchang University, Xuefu Avenue 999, Nanchang City, 330031 China;4. Department of Materials and Chemicals, School of Physics and Materials Science, Nanchang University, Xuefu Avenue 999, Nanchang City, 330031 China |
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| Abstract: | Anharmonicity of molecular vibrational motions is closely associated with the thermal property of crystals. However, the origin of anharmonicity is still not fully understood. Low-frequency vibrations, which are usually defined in the terahertz (THz) range, show excellent sensitivity to anharmonicity. In this work, anharmonicity of isonicotinamide in the form I was investigated by using temperature-dependent terahertz time-domain spectroscopy and the quasi-harmonic approximation (QHA) approach at PBE-D3 and PBE-MBD levels. Both DFT calculations suggest the variation of π-π stacking conformation dominates in the thermal expansion of the unit cell. Frequency shifts of the modes in THz range obtained by QHA approach are found to be qualitatively consistent with experimental observations, demonstrating QHA approach is a useful tool for the interpretation of frequency shifts of modes induced by temperature. |
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| Keywords: | anharmonicity density functional calculation isonicotinamide terahertz spectroscopy quasi-harmonic approximation |
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