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．     

吲哚分子振动光谱的密度泛函理论研究

用多种密度泛函理论(DFT)方法(BLYP/6-31G^*^*,B3LYP/6-31G^*^*,B3PW91/6-31G^*^*和SVWN/6-31G^*^*)对吲哚分子的平衡几何构型进行了优化。在优化构型的基础上计算了吲哚分子的谐力场、振动基频和红外光谱强度。计算得到的振动频率与实验值比较平均偏差对四种计算方法(BLYP/6-31G^*^*,P3LYP/6-31G^*^*,B3PW91/6-31G^*^*和SVWN/6-31G^*^*)分别为16.3,40.5,45.1和26.4cm^-^1。BLYP/6-31G^*^*理论力场被用于吲哚分子的简正坐标分析计算中。根据振动率的势能分布(PEDs)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。     

Si~2Cl~6分子的内旋转能垒和振动基频的理论研究

用从头算方法HF/6-31G^*^*和密度函方法B3LYP/6-31G^*^*,对Si~2Cl~6分子的平衡几何构型进行优化,优化的结果与实验结果吻合得较好.并用上述两种不同的方法计算Si~2Cl~6分子的内旋转能垒,结果分别为8.786和6.694kJ/mol,其中DFT方法的计算结果与实验结果4.18kJ/mol吻合得较好.对Si~2Cl~6分子的振动基频进行计算.用HF/6-31G^*^*SQM力场所计算的频率理论值与实验值的平均误差为7.3cm^-^1,用B3LYP/6-31G^*^*未标度的力场所计算的频率理论值与实验值的平均误差为6.0cm^-^1.该密度泛函方法(B3LYP/~6-31G^*^*)的理论计算值比用HF/6-31G^*^*标度后的SQM力场计算的频率与实验值(除Si--Si键扭转振动基频之外的11条振动基频)吻合得更好.并给出了Si--Si键扭转振动基频的预测值。     

Si~2Cl~6分子的内旋转能垒和振动基频的理论研究

用从头算方法HF/6-31G^*^*和密度函方法B3LYP/6-31G^*^*,对Si~2Cl~6分子的平衡几何构型进行优化,优化的结果与实验结果吻合得较好.并用上述两种不同的方法计算Si~2Cl~6分子的内旋转能垒,结果分别为8.786和6.694kJ/mol,其中DFT方法的计算结果与实验结果4.18kJ/mol吻合得较好.对Si~2Cl~6分子的振动基频进行计算.用HF/6-31G^*^*SQM力场所计算的频率理论值与实验值的平均误差为7.3cm^-^1,用B3LYP/6-31G^*^*未标度的力场所计算的频率理论值与实验值的平均误差为6.0cm^-^1.该密度泛函方法(B3LYP/~6-31G^*^*)的理论计算值比用HF/6-31G^*^*标度后的SQM力场计算的频率与实验值(除Si--Si键扭转振动基频之外的11条振动基频)吻合得更好.并给出了Si--Si键扭转振动基频的预测值。     

FC(O)NCS 分子振动光谱的理论研究

采用DFT(B3LYP)方法,以6-3G*为基组对FC(O)NCS的顺式和反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*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FC(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。     

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.     

氟磺酸氯分子振动光谱的从头算研究

采用从头算HF方法以6-31G^*基组研究了对ClOSO₂F分子的几何结构、振动谐性力场和红外光谱.理论力场由Pulay的标度量子力学方法进行标度,算得的振动频率与实验值比较,平均偏差为6.0cm^-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.     

Si2Br6的分子振动光谱的理论研究

用量化从头算方法(HF/6-31G^*)和密度泛函方法(B3LYP/6-31G^*)以6-31G标准基组加一个极化函数,对Si₂Br₆分子的平衡几何构型和振动频率分别进行优化和计算,优化的结果与实验结果吻合得较好.按照Pulay的建议对HF/6-31G^*水平上所计算的谐性力场进行标度(标度因子取0.9).用HF/6-31G^*SQM力场所计算的基频预测值和实验值的平均误差为9.4cm^-1,最大误差为23.6cm^-1;用B₃LYP/6-31G^*未标度力场所计算的基频预测值和实验值的平均误差为8.6cm^-1,最大误差为16.6cm^-1;用该密度泛函方法所计算的基频预测值比用HF/6-31G^*的标度后的SQM力场所计算的基频预测值和实验值(除Si-Si键扭转振动基频之外的11条振动基频)吻合得更好.HF/6-31G^*和B3LYP/6-31G^*计算给出Si-Si键扭转振动基频的预测值分别为14cm^-1和9cm^-1.     

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.     

Theory Study on Structures and Vibrational Frequencies of Pyruvic acid

Anumberoftheoreticalstudiesexistforpyruvicacid.IthasbeenstudiedatthesemiempiricalINDOandAMIlevell'2.AttheahinitiolevelstudiesofpyruvicacidrangefromthecalculationofenergiesattheSTO-3Glevel'tocalculationsofenergiesusingtheHF/3-2iG',HF/4-21G',HF/6-3iG*andMP2/4-21Gmethods.ExceptforthestudyofMurtoetal.,allthestudieshavefocussedontheenergiesandgeometriesofpyruvicacid.Moreoveralltheexistingtheoreticalstudieshavefocusedtheirattentionontheorientationofthecarboxylhydrogenextensively.Theorienta…     

Theoretical Study on the Structure and Vibrational Spectra for4-methyl-3-penten-2-one

The4-methyl-3-penten-2-oneisanimportanta,0-unsaturedketonemoleculeandanimportantligandoftheorganometalliccompounds.Untilnow,somepropertiesofphoto-chemistryandexcitedstateshavebeenexperimentallystudied'-#andconformationofthemoleculewerealsostudiedinexperiments"'.Standardinfraredgratingspectrumwasalsoobtainedin1970'.However,therearenodensityfunctionaltheory(DFT)calculationsofthismoleculeintheliterature.Recently,densityfunctionaltheoryhasbeenacceptedbytheahinitioquantumchemistrycommunityasacost…     

Density functional theory study of vibrational spectra of acridine and phenazine

Density functional theory (DFT) calculations using Becke's exchange in conjunction with Lee-Yang-Parr's correlation functionals (BLYP), Becke's three-parameter hybrid DFT/HF method using Lee-Yang-Parr's correlation functionals (B3LYP) and ab initio Hartree-Fock (HF) method have been carried out to investigate the structure and vibrational spectra of acridine and phenazine. Structural parameters obtained by B3LYP/6-31G* geometry optimization are in good agreement with available experimental data. The raw BLYP non-CH stretching frequencies approximate the experimental results much better than the HF results with the mean absolute deviation about 16 cm(-1). The scaled B3LYP frequencies are more reliable than that of the BLYP and HF methods with the mean absolute deviation about 17 cm(-1). On the basis of the comparison between calculated and experimental results, assignments of fundamental vibrational modes are examined. Also the structure and vibrational frequencies are compared with those of anthracene, pyridine and benzene to study the similarities and differences.     

Tert-butyl N-(2-bromocyclohex-2-enyl)-N-(2-furylmethyl)carbamate的结构和振动光谱

The molecular structure, conformafional stability, and vibrational frequencies of ten-butyl N-（2- bromocyclohex-2-enyl）-N-（2-furylmethyl）carbamate （TBBFC） were investigated by utilizing the Hartree-Fock （HF） and density functional theory （DFT） ab initio calculations with 6-31G ^＊ and 6-31G^＊ ＊ basis sets. The optimized bond length and angle values obtained by HF method showed the best agreement with the experimental values. Comparison of the observed and calculated fundamental vibrational frequencies indicated that B3LYP was superior to the scaled HF approach for molecular problems. Optimal uniform scaling factors calculated for the title compound are 0.899/0.904, 0.958/0.961, and 0.988/0.989 for HF, B3LYP, and BLYP （6-31G ^＊/6-31G ^＊ ＊）, respectively.     

Theoretical study on infrared vibrational spectra of boric-acid in gas-phase using density functional methods

Density functional theory (DFT) methods with various exchange-correlation functionals such as SVWN, BVWN, BVWN5, BLYP, B1LYP, B3LYP, B3PW91, and BH and H are employed in a theoretical study of molecular boric-acid in gas-phase. In the calculations, the split valence 6-311++G** and 6-31G* basis sets were used. The geometry, zero-point vibrational energies (ZPVEs), and harmonic infrared vibrational (IR) frequencies are predicted. The calculated C_3h-symmetry geometrical parameters are compared with Hartree–Fock (HF) calculation results and experimental data. IR frequencies predicted by the BLYP, B3LYP, and B3PW91 calculations are in good agreement with experimental data. The frequency calculations presented here also suggest that the C_3h-symmetrical structure corresponds to a minimum in the potential energy surface, but neither is D_3h- or C₃-symmetrical structure.     

Density functional theory study on the structure and vibrational frequencies of glycylglycine

Eleven possible conformers of glycylglycine have been studied by using the BLYP, B3LYP methods of density functional theory and the HF method at the basis set of 6-311++G**. BLYP (using Becke's and Lee-Yang-Parr's correlation functionals), ab initio Hartree-Fock (HF) and hybrid DFT/HF B3LYP calculations have been carried out to study the structure and vibrational spectra of glycylglycine. Glycylglycine crystal structure has been determined by X-ray diffraction analysis. The title compound has been crystallizes in the orthorhombic space group C1, with Z=4. And the unit cell parameters are: a=8.1184(12)A, b=9.5542(14)A, c=7.8192(11)A and V=577.95(15)A(3). Molecular conformation calculations have got 11 possible conformers. In these possible conformers, the most stable one has been selected. The BLYP/6-311++G** and scaled HF/6-311++G** frequencies correspond well with available experimental assignments of the normal vibrational modes. Comparison of the observed fundamental vibrational frequencies of glycylglycine and calculated results by density functional B3LYP and Hartree-Fock (HF) methods indicates that B3LYP is superior to the scaled Hartree-Fock (HF) for molecular vibrational issues.     

Structure and vibrational frequencies of 2-butanimine

The conformational behavior and structural stability of 2-butanimine were investigated by utilizing ab initio calculations with 6-311++G** basis set at HF, MP2, B3LYP and BLYP levels. The vibrational frequencies of 2-butanimine were computed. Complete vibrational assignments were made on the basis of normal coordinate calculations for stable conformer of the molecule. HF results without scaled quantum mechanical (SQM) force field procedure considered are in bad agreement with experimental values. Of the two DFT methods, BLYP reproduces the observed fundamental frequencies most satisfactorily with the mean absolute deviation of the non-CH stretching modes less than 21.3 cm(-1). The results indicate that BLYP calculation is a very promising approach for understanding the observed spectral features.     

Density functional theory study of vibrational spectra. 8. Assignment of fundamental vibrational modes of 9,10-anthraquinone and 9,10-anthraquinone-d8

Density functional theory (using Becke's exchange and Lee-Yang-Parr's correlation functionals (BLYP)) and ab initio Hartree-Fock calculations were carried out in order to investigate the molecular structure and vibrational spectra of 9,10-anthraquinone and its perdeuterated analog. The calculated structural and spectral features are in good agreement with the available experimental results. Most of the BLYP/6-31G* non-CH(D) stretching frequencies are slightly lower than reliable experimental assignments; the mean absolute deviation is about 14 cm⁻¹. On the basis of agreement between calculated and experimental results, assignments of the fundamental vibrational modes were examined and some reassignments were proposed. The calculated results can serve as a guide for a future experimental search for the missing fundamentals of the target molecules.