丙酮酸分子结构与振动光谱的密度泛函理论研究

用密度泛函方法BLYP、B3LYP和从头算Hartree-Fock(HF)方法在6-31G*基组水平上对丙酮酸分子的几何结构（甲基的重叠式和交错式两种构象）和振动光谱分别进行了优化和计算,并给出了各种频率所对应的红外强度及拉曼活性,对光谱进行了指认。结果表明：在丙酮酸分子的两种构象中,重叠式比较稳定*B3LYP计算得到的构型参数与实验结果比较一致;在振动频率的计算中,BLYP未标度力场所计算的非CH3伸缩振动基频预测值和实验值的平均绝对偏差为10.4cm-1;而HF标度力场的平均绝对偏差为17.9cm-1。说明两者的结果与实验观测频率比较吻合,但B3LYP的频率计算值偏差（38.3cm-1）较大。根据振动频率的势能分布和红外光谱强度对此分子的振动基频进行了理论归属。     

N-萘基氨基甲酸甲酯振动光谱的理论研究

采用HF和DFT(B3LYP)方法及6-31G基组对N-萘基氨基甲酸甲酯的几何构型、振动谱性力场和红外光谱进行了研究,使用Pulay标度法对HF/6-21G和B3LYP/6-31G的理论力场进行标度。根据标度后的理论力场进行了简正坐标分析,得到势能分布和红外振动频率,与红外频率实验相比较,HF方法和DFT(B3LYP)方法的误差分别为37.8cm^-^1和8.68cm^-^1,此外,还根据B3LYP方法得到的势能分布和红外光谱强度对N-萘基氨基甲酸甲酯的振动基频进行了理论归属,并对前人的频率指认进行了修正和补充。     

磷酸可待因的振动光谱研究

运用密度泛函理论(DFT)计算了磷酸可待因的拉曼和红外光谱.采用B3LYP混合泛函和6-31G基函数组,同时在实验上测量了磷酸可待因的常规拉曼光谱(NRS)和红外吸收光谱(IRS),结果表明:在振动频率上理论结果与实验结果相当一致,根据理论计算的结果对磷酸可待因的振动光谱进行分析,通过理论与实验数据的比较,对磷酸可待因的所有振动谱带进行了全面地归属.     

氟磺酸氟振动光谱的从头算

采用从头算HF／SCF方法以6-31G基组研究了FOSO2F分子的几何结构、振动谐性力场和红外光谱强度．理论力场由Pulay的标度量子力学方法进行标度,计算得到的振动频率与实验值比较平均偏差为6．3cm-1．根据振动频率的势能分布和从头算红外光谱强度值对此分子的振动基频进行了理论归属．     

去氢抗坏血酸分子振动光谱的理论研究

采用RHF, MP2, DFT(B3LYP)方法, 以6-311++G**为基组研究了去氢抗坏血酸分子(DHA)的平衡几何构型和振动光谱. 计算结果表明, 采用RHF, B3LYP以及MP2 方法优化得到的几何结构以及频率值是一致的. 采用B3LYP/6-311++G**计算了DHA分子平衡构型下的谐振动力场﹑振动频率和振动强度. 使用Wilson的GF矩阵方法对DHA分子进行了简正坐标分析, 依据所得的势能分布对DHA分子的振动基频进行了合理的理论归属.     

白花丹素分子结构和红外光谱的密度泛函理论研究

白花丹素(5-羟基-2-甲基-1,4-萘醌)是中药白花丹的主要成分之一,是一种具有抗肿瘤活性的萘醌类化合物.采用密度泛函(DFT)B3LYP/6-31+G(d)方法对白花丹素分子的几何构型进行全优化,得到其几何构型参数,进一步计算得到白花丹素的红外振动光谱.对计算得到的振动频率进行归属和解析并与文献值比较,发现理论计算...     

CIC（O）NCS分子筛振动光谱的理论研究

采用密度泛函理论DFT（B3LYP）方法,以6－31G为基组对CIC（O）NCS的反式和顺式两种构型的几何结构、振动谐性力场和红外光谱进行了研究 。B3LYP／6－31G的理论力场由适用于B3LYP／6－31G计算水平和大多数有机分子的一套固定标度因子进行标度,根据标度后的理论力场进行简正坐标分析得到的势能分布（PED）和红外光谱强度值对CIC（O）NCS分子物顺式和反式两种构型的振动基频进行了理论归属。     

三(4-硝基苯基)甲烷衍生物的结构和振动光谱的理论研究（英文）

用密度泛函理论优化了三苯甲烷(1)和一系列三(4-硝基苯基)甲烷衍生物2,3和4的几何结构,并计算了其红外光谱和拉曼光谱;通过与实验光谱的对比,对实验光谱中的谱峰进行了指认,并从理论上纠正了部分对3和4红外光谱谱峰不合适的实验指认;同时预测了2,3和4的拉曼光谱.结果表明,几种化合物的振动光谱计算结果与相应的实验结果吻合良好;且化合物2,3和4的拉曼光谱具有相似性.     

鸟嘌呤红外光谱的密度泛函理论研究──标度量子力学(SQM)力场处理

用密度泛函理论DFT(B3LYP)/6-31G^*方法对鸟嘌呤分子的酮-胺式和醇-胺式异构体的几何结构、振动谐性力场和红外光谱进行了研究.理论力场由迁移自相关分子异胞嘧啶和咪唑的力常数标度因子进行标度.算得振动频率与鸟嘌呤的实验基质隔离IR光谱比较平均偏差对酮-胺式和醇-胺式分别为6.6和6.0cm^-1.根据振动频率的势能分布和DFT计算的光谱强度值对鸟嘌呤分子的实验振动基频进行了理论归属.     

ClC(O)NCS分子振动光谱的理论研究

采用密度泛函理论DFT(B3LYP)方法,以6-31G^*为基组对ClC(O)NCS的反式和顺式两种构型的几何结构、振动谐性力场和红外光谱进行了研究.B3LYP/6-31G^*的理论力场由适用于B3LYP/6-31G^*计算水平和大多数有机分子的一套固定标度因子进行标度.根据标度后的理论力场进行简正坐标分析得到的势能分布(PED)和红外光谱强度值对ClC(O)NCS分子的顺式和反式两种构型的振动基频进行了理论归属.     

氰乙基对几种芳胺结构和光谱的影响

采用量子化学中密度泛函理论(DFT)的B3LYP方法分别用6-31G*和6-311+G*基组对苯胺、对氯苯胺和对甲苯胺及其氰乙基衍生物的几何构型进行全优化, 探讨了氨基上氰乙基的引入对分子电荷转移、前线轨道能量和电子光谱等性质的影响规律. 在此基础上采用含时密度泛函方法(TD-DFT)计算了分子第一激发态的电子跃迁能, 得到最大吸收波长λmax. 计算结果表明, 氨基上氰乙基的引入, 对前线分子轨道组成影响虽然小, 但使得最大吸收波长红移, 与实验值λmax有较好的一致性, 发现该类物质主要吸收光谱源于分子内的π→π*的电子跃迁.     

Computational modeling of a stereoselective epoxidation: reaction of carene with peroxyformic acid

Electronic structure theory was used to model the epoxidation of 3-carene by peroxyformic acid. Reactants, products, and transition states were optimized at the B3LYP/6-31G* level of theory, followed by B3LYP/6-311+G** and MP2/6-311+G** single point calculations. The reaction pathway yielding the trans-epoxide product was found to have a significantly lower reaction barrier (7.8 kcal/mol) than that leading to the cis-epoxide product (9.4 kcal/mol), in agreement with expectations. Magnetic shieldings of the two isomeric carene epoxides were also calculated, using the GIAO method, and compared to experimental (1)H and (13)C NMR spectra. Although the calculated carbon spectra proved inconclusive, the proton shieldings calculated for the trans-epoxide correlated much more closely to the experimental values for the major epoxidation product than did the shieldings calculated for the cis-epoxide, serving to verify the identity of the major product.     

二苯基乙二酮结构和电子光谱的理论研究

基于二苯基乙二酮结构优化,在TD-B3LYP/6-31+G*水平上讨论了两个异构体在气相和液相中的吸收和发射光谱.溶液中的计算采用可极化连续介质模型.结果表明,溶剂极性增加更有利于顺式非平面构型的形成,两个异构体的T1和S1态以及顺式非平面结构的S2态都源于双羰基上的n→π*.     

Density functional theory studies on the electronic and vibrational spectra of octaethylporphyrin diacid

The ground-state structure and electronic and vibrational spectra of octaethylporphyrin diacid (H4OEP2+) have been studied with the density functional theory. The geometrical parameters computed with B3LYP, PBE1PBE and mPW1PW91 functionals and 6-31G* basis sets are well consistent with the experimental values. Electronic absorption spectrum of H4OEP2+ has been studied with the time-dependent DFT method, and the calculated excitation energies and oscillator strengths are compared with the experimental results. The Raman and IR spectra of H4OEP2+ and the Raman spectrum of its N-deuterated analogue (D4OEP2+) were measured. The observed Raman and IR bands have been assigned based on the frequency calculations at the B3LYP/6-31G* level of theory.     

Density functional theory study on the structure and vibrational spectra for cyanuric chloride

The molecular structure and vibrational spectra of cyanuric chloride have been investigated by density functional theory (DFT) using standard B3LYP/6-31G* and B3LYP/6-311+G** method and basis set combinations. The DFT force field transformed to natural internal coordinates was corrected by a well-established set of scale factors that were found to be transferable to the title compound. Both the calculated structural parameters and vibrational frequencies are in good agreement with the available experimental data.     

Structure and conformational stability of CH2CHCH2X (X=F, Cl and Br) molecules—post Hartree–Fock and density functional theory methods

The molecular structure and conformational stability of CH₂CHCH₂X (X=F, Cl and Br) molecules were studied using ab initio and density functional theory (DFT) methods. The molecular geometries of 3-fluoropropene were optimized employing BLYP and B3LYP levels of theory of DFT method implementing 6-311+G(d,p) basis set. The MP2/6-31G^*, BLYP and B3LYP levels of theory of ab initio and DFT methods were used to optimize the 3-chloropropene and 3-bromopropene molecules. The structural and physical parameters of the molecules are discussed with the available experimental values. The rotational potential energy surface of the above molecules were obtained at MP2/6-31G^* and B3LYP/6-311+G(d,p) levels of theory. The Fourier decomposition of the rotational potentials were analyzed. The HF/6-31G^* and MP2/6-31G^* levels of theory have predicted the cis conformer as the minimum energy structure for 3-fluoropropene, which is in agreement with the experimental values, whereas the BLYP/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels of theory reverses the order of conformation. The ΔE values calculated for 3-chloropropene at MP2/6-31G^*, BLYP/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels of theory show that the gauche form is more stable than the cis form, which is in agreement with the experimental value. The same levels of theory have also predicted that the gauche form is stable than cis for 3-bromopropene molecule. The maximum hardness principle has been able to predict the stable conformer of 3-fluoropropene at HF/6-31G^* level of theory, but the same level of theory reverses the conformational stability of 3-chloropropene and 3-bromopropene molecules and MP2/6-31G^* level of theory predicted the stable conformer correctly.     

Conformational study of the structure of 12-crown-4-alkali metal cation complexes

A conformational search was performed for the 12-crown-4 (12c4)-alkali metal cation complexes using two different methods, one of them is the CONFLEX method, whereby eight conformations were predicted. Computations were performed for the eight predicted conformations at the HF/6-31+G*, MP2/6-31+G*//HF/6-31+G*, B3LYP/6-31+G*, MP2/6-31+G*//B3LYP/6-31+G*, and MP2/6-31+G* levels. The calculated energies predict a C4 conformation for the 12c4-Na+, -K+, -Rb+, and -Cs+ complexes and a C(s) conformation for the 12c4-Li+ complex to be the lowest energy conformations. For most of the conformations considered, the relative energies, with respect to the C4 conformation, at the MP2/6-31+G*//B3LYP/6-31+G* are overestimated, compared to those at the MP2/6-31+G* level, the highest level of theory considerd in this report, by 0.2 kcal/mol. Larger relative energy differences are attributed to larger differences between the B3LYP and MP2 optimized geomtries. Binding enthalpies (BEs) were calculated at the above-mentioned levels for the eight conformations. The agreement between the calculated and experimental BEs is discussed.     

Comparative studies on the structures,infrared spectrum,and thermodynamic properties of phthalocyanine using ab initio Hartree–Fock and density functional theory methods

The molecular structure, vibrational spectrum, standard thermodynamic functions, and enthalpy of formation of free base phthalocyanine (Pc) have been studied using the density functional theory B3LYP procedure, as well as the ab initio Hartree–Fock method. Various basis sets 3‐21G, 6‐31G*, and LANL2DZ have been employed. The results obtained at various levels are discussed and compared with each other and with the available experimental data. It is shown that calculations performed at the Hartree–Fock level cannot produce a reliable geometry and related properties such as the dipole moment of Pc and similar porphyrin‐based systems. Electron correlation must be included in the calculations. The basis set has comparatively less effect on the calculated results. The results derived at the B3LYP level using the smaller 3‐21G and LANL2DZ basis sets are very close to those produced using the medium 6‐31G* basis set. The geometry of Pc obtained at the B3LYP level has D_2h symmetry and the diameter of the central macrocycle is about 4 Å. The enthalpy of formation of Pc in the gas phase has been predicted to be 1518.50 kJ/mol at the B3LYP/6‐311G(2d,2p)//B3LYP/6‐31G* level via an isodesmic reaction. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

蒽醌及其羟基衍生物的密度泛函理论研究

运用密度泛函理论, 在B3LYP/6-31G*水平上, 对蒽醌及其羟基取代衍生物进行理论计算. 几何全优化的结果表明, 标题化合物均取平面构型, 分子内氢键对几何构型和电子结构影响很大. 基于简谐振动分析求得IR谱频率和强度, 并作了对称性分类和指认, 计算值与实验值良好相符. 运用含时密度泛函理论方法在相同水平上计算了标题物的电子吸收光谱, 发现蒽醌芳环取代衍生物的最低激发单重态均源自HOMO-LUMO(π→π*)跃迁. 基于振动分析, 由统计热力学求得了标题物的热力学性质.     

噻唑类生色分子的电子光谱和非线性光学性质

在B3LYP/6-31+G*水平上对八种噻唑类生色分子的电子光谱与二阶非线性光学性质茁进行计算研究. 结果表明, 含羟乙基、烷氧乙基、氟乙基和氨乙基活性基团的噻唑类分子具有大的β值, 为1.6×10-28 esu左右, 与实验结果基本一致. 气相中的最大吸收波长λmax位于480-488 nm范围内. 含羟乙基活性基团的噻唑分子, 随溶剂极性增大, λmax有红移趋势.