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  本文選題：太赫茲光譜　切入點：密度泛函理論　出處：《電子科技大學》2017年碩士論文　論文類型：學位論文

【摘要】：太赫茲光譜包含著豐富的物質結構信息,在材料鑒別、定量分析以及分子構象動力學等諸多基礎與應用研究領域有著重要的應用。與無機材料相比,有機物在太赫茲波段的研究更為活躍。有機物的集體振動模式處于太赫茲波段,且種類繁多、易于設計成高效的太赫茲發(fā)射源和敏感的探測材料。然而,有機物的太赫茲振動模式尤為復雜,難于進行深入的分析和理解。這不僅不利于太赫茲光譜技術在表征和分析有機材料方面的應用,而且嚴重阻礙了探索性能優(yōu)異的太赫茲新材料的步伐。為此,本文結合太赫茲光譜儀和基于密度泛函理論(DFT)的光譜計算,研究了纖維素及其同素異形體、氫鍵分子晶體�；撬嵋约坝袡C磺酸鹽DAST的太赫茲光譜及其響應原理,探究了固態(tài)DFT在準確預測部分結晶聚合物和氫鍵分子晶體太赫茲光譜的計算方法。本論文的主要成果包括:(1)采用低溫溶解法制備了再生纖維素薄膜,對其物理形貌、結晶類型和化學成分進行了表征。首次指認并歸屬了再生纖維素(纖維素II)在0.1-21 THz波段的太赫茲指紋譜峰,提出一種利用太赫茲光譜來有效鑒別纖維素Iβ和纖維素II同素異晶體的新方法。指出再生纖維素的低頻吸收峰源于其有序結晶部分的分子振動,據(jù)此提出一種適用于部分結晶聚合物光譜計算建模的簡化處理方法。(2)以相對簡單的氫鍵分子晶體�；撬釣檠芯繉ο�,指出固定晶格法和色散校正完全弛豫法在處理分子間相互作用方面的不同是導致兩種方法預測的太赫茲光譜間差異的主要原因,揭示了色散校正在模擬氫鍵分子系統(tǒng)太赫茲光譜中的重要作用。首次指認并歸屬了固態(tài)�；撬嵩�3-12 THz波段的太赫茲特征峰,還研究了�；撬崽掌澒庾V的溫度動力學特性,據(jù)此提出一種新型的三振子耦合模型合理地解釋了實驗上觀測到的太赫茲特征峰隨溫度升高的反常藍移現(xiàn)象。(3)采用逐步提高收斂精度的分步優(yōu)化法,獲得與實驗一致的DAST基態(tài)結構,為進一步的模式分析提供了支持。首次對DAST太赫茲低頻振動模式進行分析。結果表明1.12 THz處的振動是陰陽離子的光學聲子模式,1.46 THz和1.54 THz兩處的振動主要與磺酸鹽陰離子有關,2.63 THz和3.16 THz處的振動源于陽離子的扭轉振動和陰離子的轉動。這些模式分析彌補了DAST太赫茲聲子模式分析的空白,為今后設計合成具有二階非線性的DAST衍生物提供了重要的參考和指導。
[Abstract]:The terahertz spectrum contains abundant material structure information and has important applications in the fields of material identification, quantitative analysis and molecular conformational kinetics. Organic compounds are more active in the terahertz band. The collective vibration modes of organic compounds are in the terahertz band, and they are easily designed as efficient terahertz emitters and sensitive detection materials. The terahertz vibration mode of organic compounds is particularly complex and difficult to be analyzed and understood in depth, which is not only unfavorable to the application of terahertz spectroscopy in the characterization and analysis of organic materials. Therefore, the study of cellulose and its isomorphism is based on the spectral calculation of terahertz spectrometer and density functional theory (DFT). Terahertz Spectra of hydrogen bonded Molecular Crystal taurine and Organic sulfonate DAST and its response principle, The calculation method for accurate prediction of terahertz spectra of some crystalline polymers and hydrogen-bonded molecular crystals by solid DFT has been investigated. The main achievements in this paper include: 1) the regenerated cellulose films were prepared by low temperature dissolution method and their physical morphology was investigated. The crystalline type and chemical constituents were characterized. The terahertz fingerprint peak of regenerated cellulose (Cellulose II) at the wavelength of 0.1-21 THz was identified and assigned for the first time. A new method for the identification of cellulose I 尾 and cellulose II isomers by using terahertz spectrum is proposed. It is pointed out that the low frequency absorption peak of regenerated cellulose originates from the molecular vibration of its ordered crystalline part. A simplified processing method for spectral modeling of partially crystallized polymers is proposed. The relatively simple hydrogen-bonded molecular crystal taurine is used as an object of study. It is pointed out that the difference between the fixed lattice method and the complete dispersion correction relaxation method in the treatment of intermolecular interaction is the main reason for the difference between the terahertz spectra predicted by the two methods. The important role of dispersion correction in the terahertz spectrum of the simulated hydrogen bond molecular system is revealed. The terahertz characteristic peaks of solid taurine in the 3-12 THz band are identified and assigned for the first time. The thermodynamics of the taurine terahertz spectrum is also studied. Based on this, a new coupling model of three oscillators is proposed to reasonably explain the abnormal blue shift phenomenon of terahertz characteristic peak observed in experiments with increasing temperature. The stepwise optimization method is used to improve the convergence accuracy step by step. The ground state structure of DAST is obtained, which is consistent with the experiment. It is the first time to analyze the low frequency vibration mode of DAST terahertz. The results show that the vibration at 1.12 THz is the optical phonon mode of anion and anion at 1.46 THz and 1.54 THz mainly with sulfonic acid. The vibration of salt anions at 2.63 THz and 3.16 THz originates from the torsional vibration of cations and the rotation of anions. These model analyses make up the gaps in the analysis of DAST terahertz phonon modes. It provides an important reference and guidance for the design and synthesis of DAST derivatives with second order nonlinearity.
【學位授予單位】：電子科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：O636.11;O623.84

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本文編號：1630723