CAJ | 학술논문

利用量子化学计算方法模拟物质的太赫兹吸收谱，可以为目标物质的太赫兹吸收特征匹配分子振动模式，对深刻理解谱的形成机理十分必要。模拟结果的可靠性，主要取决于目标物质初始构型的搭建和振动模式计算方法的选择。首先利用太赫兹时域光谱技术获取了谷氨酰胺固态样品的太赫兹吸收谱，为了在理论模拟过程中体现考虑分子间作用的程度，构建了三种常用于有机物太赫兹吸收谱模拟的谷氨酰胺初始构型，单分子、二聚体、晶胞。使用量子化学计算程序基于密度泛函理论对三种初始构型进行了结构优化和振动模式计算。将计算结果通过洛伦兹线型函数拟合为吸收谱与实验吸收谱进行对比发现，二聚体构型的模拟吸收谱从吸收峰个数上优于单分子构型，在此基础上，晶胞构型模拟结果从吸收峰峰位上又较二聚体构型有了明显的改进，随着初始构型考虑分子间作用的程度提高模拟结果逐步逼近实验吸收谱。在得到了可靠的理论模拟吸收谱的基础上，成功对谷氨酰胺固态样品在0.3～2.6 T Hz范围内的三个吸收峰匹配了晶胞内各分子的集体振动模式。研究表明，在固体样品的太赫兹吸收谱理论模拟中，在计算能力允许的情况下，应尽可能选择全面反映分子间作用力的晶胞构型作为计算的初始构型。
이용양자화학계산방법모의물질적태혁자흡수보，가이위목표물질적태혁자흡수특정필배분자진동모식，대심각리해보적형성궤리십분필요。모의결과적가고성，주요취결우목표물질초시구형적탑건화진동모식계산방법적선택。수선이용태혁자시역광보기술획취료곡안선알고태양품적태혁자흡수보，위료재이론모의과정중체현고필분자간작용적정도，구건료삼충상용우유궤물태혁자흡수보모의적곡안선알초시구형，단분자、이취체、정포。사용양자화학계산정서기우밀도범함이론대삼충초시구형진행료결구우화화진동모식계산。장계산결과통과락륜자선형함수의합위흡수보여실험흡수보진행대비발현，이취체구형적모의흡수보종흡수봉개수상우우단분자구형，재차기출상，정포구형모의결과종흡수봉봉위상우교이취체구형유료명현적개진，수착초시구형고필분자간작용적정도제고모의결과축보핍근실험흡수보。재득도료가고적이론모의흡수보적기출상，성공대곡안선알고태양품재0.3～2.6 T Hz범위내적삼개흡수봉필배료정포내각분자적집체진동모식。연구표명，재고체양품적태혁자흡수보이론모의중，재계산능력윤허적정황하，응진가능선택전면반영분자간작용력적정포구형작위계산적초시구형。
With simulation of absorption spectra in T Hz region based on quantum‐chemical calculation ,the T Hz absorption fea‐tures of target materials can be assigned with theoretical normal vibration modes .This is necessary for deeply understanding the origin of THz absorption spectra .The reliabilities of simulation results mainly depend on the initial structures and theoretical methods used throughout the calculation .In our study ,we utilized THz‐TDS to obtain the THz absorption spectrum of solid‐state L‐glutamine .Then three quantum‐chemical calculation schemes with different initial structures commonly used in previous studies were proposed to study the inter‐molecular interactions’ contribution to the THz absorption of glutamine ,containing monomer structure ,dimer structure and crystal unit cell structure .After structure optimization and vibration modes’ calculation based on density functional theory ,the calculation results were converted to absorption spectra by Lorentzian line shape function for visual comparison with experimental spectra .The result of dimmer structure is better than monomer structure in number of absorption features while worse than crystal unit cell structure in position of absorption peaks .With the most reliable simulation result from crystal unit cell calculation ,we successfully assigned all three experimental absorption peaks of glutamine ranged from 0.3 to 2.6 THz with overall vibration modes .Our study reveals that the crystal unit cell should be used as initial structure during theoretical simulation of solid‐state samples’ THz absorption spectrum which comprehensively considers not only the in‐tra‐molecular interactions but also inter‐molecular interactions .