铝原子团簇Al5、Al5-和Al5+稳定结构的密度泛函理论研究

采用密度泛函理论的四种方法 :杂化密度泛函B3LYP与B3PW 91、Perdew Wang91交换与相关泛函WP91PW91、局域自旋密度近似SVWN ,研究了Al5、Al5-和Al5+ 团簇的多种可能结构 ,找到了它们稳定的结构与自旋态 ,与已有的理论结果作了比较 ,并计算了Al5-的绝热与垂直电子离解能、Al5的绝热与垂直电离势 ,同有关的实验数据比较 ,符合较好 .同时对四种密度泛函方法的计算结果作了一些比较与讨论     

Hole trapping at Al impurities in silica: a challenge for density functional theories

The atomic geometry and electronic structure around a neutral substitutional Al impurity in silica is investigated using either the unrestricted Hartree-Fock (UHF) approximation, or Beckes three-parameter hybrid functional (B3LYP). It is found that the B3LYP functional fails to describe the structural distortions around the Al impurity, while the UHF results are consistent with experimental information. We argue that the failure of the B3LYP functional is caused by the incomplete self-interaction cancellation usually present in density functional theories.     

Multiplet splittings and other properties from density functional theory: an assessment in iron–porphyrin systems

In transition metal compounds with spin states close in energy, the magnitude and sign of the energy splitting calculated with density functional theory depends strongly on the functional used. Therefore we must turn to additional criteria to assess the level of accuracy and reliability of predictions based on this level of theory. We report optimized geometries, total energies, and Mössbauer quadrupole splitting values for low-spin and high-spin, ferric and ferrous model hemes using a variety of gradient-corrected and hybrid functionals. In one model, the iron–porphyrin is axially ligated by two strong-field imidazole ligands [FeP(Im)₂] and has a low-spin ground state. In the other model complex the axial ligands are two weak-field, water molecules [FeP(H₂O)₂], and have a high-spin ground state. Among all the functionals used (UHF, B3LYP, B3LYP*, BLYP, half-and-half, LSDA), the B3LYP hybrid functional most consistently reproduced the experimental geometry, Mössbauer, and spin state data for the two model hemes. Simply gradient-corrected functionals exhibit strong biases towards low spin states, while Hartree–Fock favours strongly high spin states. These findings suggest that for systems with similar characteristics of several accessible electronic spin configurations, it is imperative to include properties other than just the energy in the assessment of the DFT predictions.     

The importance of the self-interaction correction for Jahn–Teller distortion of the zinc vacancy in ZnGeP2

A cluster model is used to investigate the zinc vacancy in zinc germanium diphosphide in unrestricted Hartree–Fock method and density functional theory (DFT) with the B3LYP functional. While DFT maintains the symmetry of the defect, Hartree–Fock method, which is self-interaction free, predicts a symmetry breaking with the defect electron localizing on a single P atom instead of being equally spread over the four neighboring P atoms. While this distortion does not yet agree with the experimental observation of a pairing of P atoms, it illustrates the importance of the self-interaction and the difficulty in identifying the true minimum energy configuration of point defects in semiconductors.     

甘氨酸与水分子间相互作用的理论研究

在密度泛函(DFT)B3LYP/6_311++G(3d,3p)水平,对中性甘氨酸的最小点结构Ip和H2O分子间可能存在的氢键复合物进行全自由度能量梯度优化,发现了三个氢键极小结构A、C和E,其中结构A为最稳定结构,它是H2O与甘氨酸的羧基(-COOH)形成两个氢键的结构,具有C1对称性.分别采用密度泛函理论(DFT)和MP2方法,在6-311++G(3d,3p)水平,对结构A的结构和结合能进行了比较计算,得到结合能ΔEDFT为-41.88 kJ/mol,ΔEMP2为-40.34 kJ/mol.     

草酰胺分子构型、稳定性、IR光谱及分子轨道的密度泛函与从头算研究

运用多种密度泛函理论 (DFT)和从头算 (abinitio)方法研究了草酰胺顺、反异构体的分子几何构型 ,结果表明Beck88交换函数与LYP非局域相关函数形成杂化的DFT方法B3LYP与MP2方法计算结果比较吻合。在此基础上选择B3LYP方法对草酰胺分子电子结构、红外光谱和前线分子轨道组成进行了系统研究 ;与实验事实对比分析了气态草酰胺分子中配位原子的反应活性     

3,4-二氯-1,2,5-噻二唑的结构及其振动光谱

实验测量了3,4-二氯-1,2,5-噻二唑分子4000～400 cm-1区域内的红外光谱和3700～100 cm-1范围内的拉曼光谱,使用密度泛函理论计算了分子的稳定结构和振动频率.以实验测定频率为标准采用简正振动分析方法得到了各振动谱带的总能量分布,从而对该分子的振动频率做出了全面归属.     

FT-IR, FT-Raman, NMR spectra and DFT simulations of 4-(4-fluoro-phenyl)-1H-imidazole

The FT-IR, FT-Raman and FT-NMR spectra of the compound 4-(4-Fluoro-phenyl)-1H-imidazole (4-FPI) were recorded and analyzed. Density functional method (B3LYP level with the 6–311G(d, p) and 6–311++G(d, p) and cc-pVQZ as basis sets) has been used to compute optimized geometry, vibrational wavenumbers of the 4-FPI. Only one tautomeric form was found most stable by using DFT/B3LYP. The detailed interpretation of the vibrational spectra was carried out with the aid of total energy distribution following the scaled quantum mechanical force field methodology. Potential Energy Surface scan studies has also been carried out by ab initio calculations with the same basis sets.     

CH3S CH2SH异化反应的理论研究

利用密度泛函理论(DFT)和从头算(ab initio)研究了CH3S←→CH2SH互异化的反应机理．采用HF、B3LYP、MP2理论水平和中等基组6-31(d)，计算了CH3S、CH2SH及其过渡态的结构参数、谐振频率、零点能(ZPF)、总能量和相对能量，并利用B3LYP／6-31(d)的方法计算了反应的内禀反应坐标(IRC)，给出了分子构型和自旋污染沿反应坐标的变化曲线，以及最小能量曲线(MEP)、绝热能量曲线．此外，利用传统过渡态理论(CTST)研究了该互异化反应的速率常数和平衡常数在200～1000K的变化．     

自由基聚合中二硫酯结构及其活性的研究

用密度泛函方法,在B3LYP/6-31G+(d)水平上对三种二硫酯化合物进行了几何构型全优化.计算了C-S键离解能以及对于自由基的原子自旋密度,并且探讨了它们与化合物活性之间的关系,分析的结论与实验结论完全一致.同时结论也表明密度泛函理论计算能为C—S键离解能,原子自旋密度变化趋势提供一个很好的预测.     

自由基聚合中二硫酯结构及其活性的研究

用密度泛函方法,在B3LYP/6-31G+(d)水平上对三种二硫酯化合物进行了几何构型全优化. 计算了C-S键离解能以及对于自由基的原子自旋密度,并且探讨了它们与化合物活性之间的关系, 分析的结论与实验结论完全一致。同时结论也表明密度泛函理论计算能为C-S键离解能,原子自旋密度变化趋势提供一个很好的预测。     

铝团簇的电子自旋极化与核自旋-自旋偶合的理论研究

利用传统的密度泛函理论在B3LYP/6-31 G(d)水平上优化了铝簇(Aln ,Aln与Aln-,n=2~9)的几何结构,并利用偶合的微扰的密度泛函理论在B3LYP/6-311 G(3df)水平上计算了核自旋-自旋偶合常数.优化结果表明Aln(n=2~9)中的电子是自旋极化的,与早期的质谱实验一致.核自旋-自旋偶合常数的计算结果表明电子的自旋极化与原子核的自旋取向有密切关系.     

Unrestricted Dirac-Fock theory: Relativistic determination of core polarization hyperfine interactions

The unrestricted Dirac-Fock (UDF) method is developed for determining relativistic contributions to the hyperfine interaction, notably that due to core polarization. Radial core-polarization of the one-electron (jj-coupled) spin orbitals is obtained by relaxing the restraint in restricted Dirac-Fock (RDF) theory that the radial part be independent of the magnetic quantum number, the projection m_j of j. Relativistic effects on the core polarization are obtained by comparison with results obtained from the non-relativistic spin polarized Hartree-Fock (m_s unrestricted) and spin plus orbital polarized Hartree- Fock (m_s plus m_j unrestricted) calculations. For the 5d transition series ions, the relativistic core polarization enhancement factor, S_s(z), is determined to be about a factor of two and so is much smaller than the isomer shift charge density enhancement factor (≈6) found earlier for these same ions. Comparison is made with limited experimental data available to date; for the case of atomic Re, excellent agreement is obtained with experiment.     

On the thermochemical stability of the sextet CO2 anion: results from density functional theory

A variety of density functional theory (DFT) methods were used to characterize the stability of stationary points along the CO^? ₂ (⁶A₁ state) potential energy surface. Large differences were found between the previously reported ROHF/CCSD structures of this molecule and those generated by DFT. The SVWN, B1LYP, B3LYP, B3P86, B3PW91, methods were coupled to a very large 6–311++G (3df, 3pd) basis set, to evaluate the vibrational frequencies, electron affinities and the lowest dissociation pathways for the two isomers of the anionic and neutral parent species. In addition to these pure and hybrid methods both the CBS-QB3 (uses the B3LYP/CBSB7 method for the geometrical optimization) and G3B3 (uses the B3LYP/6-31G(d) method for the geometrical optimization) methods were used to further evaluate the dissociation energies of the sextet anionic CO₂.     

TATB的亚稳结构的理论计算

采用密度泛函理论B3LYP方法,在6-311g**水平上对TATB的结构进行优化,得到了TATB的稳定几何结构和分子内部质子迁移后形成的亚稳结构,计算了这两个结构的电子能量.对计算结果进行了讨论.     

硝酸丙酯结构、振动频率和热力学性质的密度泛函理论研究

用密度泛函理论(DFT)研究硝酸丙酯化合物的分子结构、振动光谱和热力学等基本性质.取BLYP、B3LYP方法和6-31G*、6-31G**、6-311G*、6-311G**基组,对硝酸丙酯分子的几何构型进行全优化计算并分析其电子结构性质.和考虑了二级相关能校正的MP2/6-311G*计算结果比较表明,B3LYP/6-31G*是研究许多较大体系化合物卓有成效和颇有前途的方法.在B3LYP/6-31G*的水平上对优化后的结构进行了正则振动频率分析,用因子0.95校正后的振动光谱和实验结果比较,符合较好.进一步     

Electron momentum spectroscopy of the highest occupied molecular orbitals of chlorobromomethane

The first measurement of the complete valence shell binding energy spectra of chlorobromomethane (CH₂ BrCl) is reported by (e, 2e) electron momentum spectrometer using symmetric non-coplanar geometry at an impact energy of 1200 eV plus binding energy. The experimental electron momentum profiles of the highest occupied molecular orbitals (HOMOs) are extracted and compared with Hartree-Fock (HF) and density functional theory (DFT) calculations. DFT calculation employing B3LYP hybrid functional and the large-sized basis sets provides the best agreement with the experiment.     

Extended Hartree—Fock (EHF) theory of chemical reactions VI: hybrid DFT and post-Hartree—Fock approaches for concerted and non-concerted transition structures of the Diels—Alder reaction

Activation barrier heights for concerted and non-concerted transition structures between butadiene and ethylene have been calculated by the broken-symmetry Hartree-Fock (HF), QCISD(T), and CCSD(T) methods with and without approximate spin projection, and the spin-restricted CASCI, CASSCF UNO MP2 and MR MP2 methods. They also have been calculated by the density functional theory (DFT) and hybrid DFT (HDFT) methods such as B2LYP and B3LYP. The reliability and utility of the HDFT methods have been investigated, and compared with the post-HF and MR MP2 results. The information entropy and related electron correlation indices also have been examined in relation to the polyradical character of the transition structures. Implications of the present results are discussed concerning the applicability of HDFT to large systems.     

乙酰苯胺分子的拉曼、红外光谱和简正振动分析

分别在3 500～50和3 500～600 cm-1范围内实验测量了乙酰苯胺(ACN)分子的拉曼和红外光谱。运用密度泛函理论(DFT)采用B3LYP 混合泛函和6-311G(d, p)基函数组,计算了该分子的平衡构型和振动频率。结果表明：理论计算的分子最优化构型参数与以往文献报道的实验数据吻合,优于以往由6-31G(d)基函数组计算得到的参数;理论计算的振动频率值和本实验的观测值吻合得较好。运用简正振动分析方法得到了ACN 分子各振动频率的势能分布(PED),对ACN 分子的振动频率归属做出了全面、准确指认。     

电场作用下CaS的分子结构和电子光谱

以6-311++G(d,p)为基组,采用密度泛函的B3LYP方法优化得到不同外电场(-0·03—0·045a.u.)下CaS分子的基态结构参数、电偶极矩μ、电荷分布、HOMO能级、LUMO能级、能隙、红外光谱和谐振频率等.结果表明,随着正向电场的增加,分子结构与外电场有着强烈的依赖关系,且对电场方向的依赖呈现出不对称性,基态键长和分子偶极矩μ先减小后增大,在F=0·02a.u.时,键长Re取最小值0·2289nm,电偶极矩取最小值1·5969D,HOMO能级和LUMO能级处于先增大后减小,能隙始终是减小的,占据轨道的电子容易激发到空轨道.外电场对CaS分子的激发能和振子强度有较大的影响,这为进一步研究它的电致发光机理提供了一定的理论基础.