共查询到19条相似文献,搜索用时 78 毫秒
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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。 相似文献
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Si2Br6的分子振动光谱的理论研究 总被引:1,自引:1,他引:0
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. 相似文献
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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。 相似文献
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用密度泛函理论方法B3LYP以及6-311++G(2df,2pd)基组对2-氟-5-溴吡啶分子 的平衡几何构型进行了优化并计算了该分子的振动谐力场。使用Pulay的标度方法 对理论力场进行了标度。采用Wilson的GF矩阵方法,根据标度后的理论力场进行了 简正坐标分析,对2-氟-5-溴吡啶分子的振动基频进行了理论研究,得到了势能分 布和红外振动频率。与红外频率的实验值相比较,理论频率的均方差为24 cm~(-1) 。此外,根据振动模式的势能分布对此分子的振动基频进行了理论归属,并对前人 的指认进行了修正和补充。 相似文献
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2-氟-5-溴吡啶分子振动光谱的密度泛涵理论研究 总被引:3,自引:1,他引:2
用密度泛函理论方法B3LYP以及6-311++G(2df,2pd)基组对2-氟-5-溴吡啶分子 的平衡几何构型进行了优化并计算了该分子的振动谐力场。使用Pulay的标度方法 对理论力场进行了标度。采用Wilson的GF矩阵方法,根据标度后的理论力场进行了 简正坐标分析,对2-氟-5-溴吡啶分子的振动基频进行了理论研究,得到了势能分 布和红外振动频率。与红外频率的实验值相比较,理论频率的均方差为24 cm~(-1) 。此外,根据振动模式的势能分布对此分子的振动基频进行了理论归属,并对前人 的指认进行了修正和补充。 相似文献
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本文报道了PH2^+的一组新的ab initio计算结果。给出了PH2^+的基态(X^1A1)及几个低激发态的电子结构和几何构型。这些态的稳定构型都是在MRSD CI水平上优化得到的。在此基础上, 确定了基态到这些低激发态的跃迁能和部分跃迁的振子强度和辐射寿命。 相似文献
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以两态模型为基础,用从头算方法,在DZP[所有原子带极化函数的Dunning(9s,5p)/(3s,2p)]基组水平上对四氰基乙烯与四甲基乙烯间的电子转移进行理论计算。通过孤立给体和受体的几何构型优化,计算了给体的电离能和受体的电子亲和能。计算表明,在光诱导电荷分离之后的返回电子转移处于高放热的Marcus反转区。通过碰撞配合物的结构优化和电荷分离处理,在线性反应坐标近似下得到四甲基乙烯-四氰基乙烯配合物电荷分离反应的双势阱,进而获得反应热,键重组能,以及跃迁能。 相似文献
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Ab initio calculations predict that D3d symmetry of Si2F6 is more stable than D3h symmetry. The calculated potential barrier to internal rotation was 0.77, 0.73 and 0.78 kcal/mol using HF/6-31G*, B3LYP/6-31G* and MP2/6-31G* methods respectively, which was in good agreement with the experimental value between 0.51±0.10 and 0.73±0.14 kcal/mol. The optimized geometries, harmonic force fields, infrared intensities, Raman activities, and vibrational frequencies are reported for D3d symmetry of Si2F6 from HF/6-31G* and B3LYP/6-31G*. A normal coordinate analysis was carried out. The average error between the scaled DFT frequencies obtained from the B3LYP/6-31G* calculation and observed frequencies was 4.2 cm−1 and the average error between the scaled HF and observed frequencies was 2.2 cm−1. 相似文献
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Quantum chemistry calculations have been performed using Gaussian03 program to compute optimized geometry, harmonic vibrational
frequency along with intensities in IR and Raman spectra at RHF/6-31++G** and B3LYP/6-31++G** levels for phenobarbitone (C12H12N2O3) in the ground state. The scaled harmonic vibrational frequencies have been compared with experimental FT-IR and FT-Raman
spectra. Theoretical vibrational spectra of the title compound were interpreted by means of potential energy distributions
(PEDs) using MOLVIB program. A detailed interpretation of the infrared spectra of the title compound is reported. On the basis
of the agreement between the calculated and observed results, the assignments of fundamental vibrational modes of phenobarbitone
were examined and some assignments were proposed. The theoretical spectrograms for FT-IR and FT-Raman spectra of the title
compound have been constructed. 相似文献
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Marek J. Wjcik Marek Boczar Marzena Stoma 《International journal of quantum chemistry》1999,73(3):275-282
Theoretical simulation of the bandshape and fine structure of the νs stretching band is presented for tropolone‐H and tropolone‐D taking into account an adiabatic coupling between the high‐frequency O–H(D) stretching and the low‐frequency intra‐ and intermolecular OO stretching modes, and linear and quadratic distortions of the potential energies for the low‐frequency vibrations in the excited state of the O–H(D) stretching vibration. In order to determine the low‐frequency vibrations, the experimental spectra of the polycrystalline tropolone in the far‐infrared and the low‐frequency Raman range have been recorded for the first time. The experimental frequencies in the low‐frequency region are compared with the results of the HF/6‐31G** and Becke3LYP/6‐31G** calculations carried out for the tropolone dimer. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 275–282, 1999 相似文献
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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。 相似文献
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Yordanka Dimitrova Bistra A. Stamboliyska 《International journal of quantum chemistry》2003,92(6):506-515
The vibrational characteristics (vibrational frequencies and infrared intensities) for free and complexed CO and HONO2 have been predicted using ab initio calculations at SCF and MP2 levels with different basis sets and B3LYP/6?31G(d,p) calculations. The ab initio calculations show that the complexation between HONO2 and CO leads to two stable structures: CO … HONO2 (1A) and OC … HONO2 (1B). The changes in the vibrational characteristics from free monomers to complexes have been estimated. It was established that the most sensitive to the complexation is the stretching O? H vibration. In agreement with the experiment, its vibrational frequency in the complexes is shifted to lower frequency (Δν = ?123 cm?1). The magnitude of the wave number shift is indicative of relatively strong hydrogen‐bonded interaction. The ab initio calculations at different levels predict an increase of the infrared intensity of the stretching O? H vibration for structure 1A more than five times and for structure 1B more than nine times. The most consistent agreement between the computed values of the frequency shifts for structure 1B and those experimentally observed suggests that this structure is preferred. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
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Carteret C Labrosse A Assfeld X 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,67(5):1421-1429
The structural and vibrational properties of siloxane monomers may account in the physical and chemical properties of silicone polymers. Because disiloxane (H(3)SiOSiH(3)) is the smallest molecule in the set which runs through small siloxanes like hexamethyldisiloxane (CH(3))3SiOSi(CH(3))3 to silicone polymers, its energetic, structural and vibrational features have been investigated in detail using density functional theory (B3LYP), post Hartree-Fock methods (MP2 and CCSD(T)) and basis sets up to spdfg quality. Five conformations were considered: three bent structures with C2v (double staggered, SS, and double eclipsed, EE, conformations) and Cs symmetries, and two linear forms with D3d and D3h symmetries. At all levels of theory, the relative stability was C2v(SS) approximately C2v(EE)>Cs>D3h>D3d. The difference of energy between the two C2v conformers is lower than 0.04 kcal/mol. At the highest level of theory (CCSD(T)/cc-pVQZ), the barrier to linearisation from C(2v) to D(3h) conformers was calculated at 0.43 kcal/mol, which is extremely low. Most of the structural and vibrational features of the disiloxane do not depend on the conformation of the molecule but are strongly influenced by the SiOSi angle. Anharmonic calculations allowed, without any scaling factor, an exhaustive reinvestigation of the assignments of observed wavenumbers in the infrared and Raman spectra of gaseous disiloxane. Particularly, in the gas phase spectrum, the SiOSi symmetric and antisymmetric stretches have been assigned at 599 and 1105, 596 and 1060, 527 and 1093 cm(-1) for H(3)SiOSiH(3), H(3)Si(18)OSiH(3) and D(3)SiOSiD(3), respectively. The experimental wavenumber splitting of SiOSi symmetric and antisymmetric stretches of H(3)SiOSiH(3) gave an estimation of the SiOSi angle at around 145 degrees . Ab initio methods were revealed more accurate for structural parameters, when DFT/B3LYP was enough for spectral assignments, even at the harmonic level using a single scaling factor. 相似文献
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ThefluorosulfonylisocyanateandchlorosulfonylisocyanatemoleculesarethemostreactivemoleculesforthetransferenceoftheNCOgroupandareveryimportantinsyntheticchemistry.Duetotheirversatilityinchemicalreactions,theyhavealsobecomethesubjectofmanystructuralstudi… 相似文献