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     

硝酸甲与硝酸乙酯的结构、振动频率和热力学性质的密度函数 理论(DFT)研究

用密度函数理论(DFT)的BLYP和B3LYP方法,取6-31G,6-31G^*,6-31G^*^*,6-311G,6-311G^*和6-311G^*^*六种基组,对硝酸甲酯和硝酸乙酯的几何构型和红外振动频率进行了计算研究.结果表明,B3LYP方法在采用极化基组(6-31G^*,6-31G^*^*,6-311G^*和6-311G^*^*)时计算得到的结果均较好,适用于硝酸酯类化合物的研究.而BLYP方法无论采用何种基组均不适用;运用校正后的B3LYP/6-31G^*频率(校正因子0.975)计算得到的热力学性质(C^o~p,H^o和S^o)与实验结果较吻合。     

Theoretical studies on the effects of methods and parameterization on the calculated free energy of hydration for small molecules

Free energies of hydration (FEH) have been computed for 13 neutral and nine ionic species as a difference of theoretically calculated Gibbs free energies in solution and in the gas phase. In‐solution calculations have been performed using both SCIPCM and PCM polarizable continuum models at the density functional theory (DFT)/B3LYP and ab initio Hartree–Fock levels with two basis sets (6‐31G* and 6‐311++G**). Good linear correlation has been obtained for calculated and experimental gas‐phase dipole moments, with an increase by ～30% upon solvation due to solute polarization. The geometry distortion in solution turns out to be small, whereas solute polarization energies are up to 3 kcal/mol for neutral molecules. Calculation of free energies of hydration with PCM provides a balanced set of values with 6‐31G* and 6‐311++G** basis sets for neutral molecules and ionic species, respectively. Explicit solvent calculations within Monte Carlo simulations applying free energy perturbation methods have been considered for 12 neutral molecules. Four different partial atomic charge sets have been studied, obtained by a fit to the gas‐phase and in‐solution molecular electrostatic potentials at in‐solution optimized geometries. Calculated FEH values depend on the charge set and the atom model used. Results indicate a preference for the all‐atom model and partial charges obtained by a fit to the molecular electrostatic potential of the solute computed at the SCIPCM/B3LYP/6‐31G* level. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

B3LYP,BLYP and PBE DFT band structures of the nucleotide base stacks

DFT crystal orbital (band structure) calculations have been performed for the nucleotide base stacks of cytosine, thymine, adenine, and guanine arranged in DNA B geometry. The band structures obtained with PBE, BLYP, and B3LYP functionals are presented and compared to other related experimental and theoretical results. The influence of the quality of the basis set on the fundamental gap values was also investigated using Clementi's double ζ, 6‐31G and 6‐31G* basis sets. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Relaxed energetic maps of κ‐carrabiose: A DFT study

The B3LYP density function was used with the 6‐31G(d) basis set to perform relaxed energetic contour maps of the charged form of κ‐carrabiose in the gas phase and for the neutral form first in the gas phase and then by simulating the presence of water as solvent using the Onsager model. Only one starting conformation has been considered to perform all the calculations. Rigid energetic maps have been then constructed either by addition of diffuse or polarization functions to the basis set obtaining in that way 6‐31+G(d)//6‐31G(d), 6‐31+G(d,p)//6‐31G(d), and 6‐311++G(d,p)//6‐31G(d) energetic maps that have been carefully examined. The obtained structures corresponding to the lower energy conformers have been then fully optimized using different basis sets with the B3LYP method, a reversion in term of energy has been observed for the two first minima in the case of the charged disaccharide in the gas phase, this was attributed to the large grid of 30° that could lead to the exclusion of an intermediate value corresponding to the real minimum of energy. We thus suggest that after establishing potential energy maps it is essential to proceed to full optimizations of the lower energy conformers. Calculations using the more accurate correlated method MP2 with the 6‐31G(d) basis set have also been performed for conformers of the two disaccharides in the gas phase. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

苯并氧化呋咱稳定性和异构化的DFT和ab initio研究

运用B3LYP/6-31G(d)密度泛函理论（DFT）方法对苯并氧化呋咱、邻二亚硝基苯及其间的异构化反应进行了计算研究。结果表明,苯并氧化呋咱的分子总能量比邻二亚硝基苯的低;由苯并氧化呋咱异构为邻二亚硝基苯的正向反应活化能（Ea+=51.0kJ/mol）,与文献实测值（58.6kJ/mol）较接近,而其逆向反应活化能（Ea-=4.6kJ/mol）很小,从而揭示了苯并氧化呋咱比邻二亚硝基苯更稳定·此外,进行了HF/3-21G、HF/6-31G(d)和MP2/6-31G(d)//6-31G(d)水平下相应的计算,发现B3LYP-DFT的结果较abinitio为优。谐振动频率的B3LYP/6-31G(d)计算还支持了邻二亚硝基苯为苯并氧化呋咱“自-自”互变重排反应的中间体。     

NMR spectra, GIAO and charge density calculations of five-membered aromatic heterocycles

The B3LYP/6-31+G(d) molecular geometry optimized structures of 17 five-membered heterocycles were employed together with the gauge including atomic orbitals (GIAO) density functional theory (DFT) method at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p) and B3LYP/6-311+G(2d,p) levels of theory for the calculation of proton and carbon chemicals shifts and coupling constants. The method of geometry optimization for pyrrole (1), N-methylpyrrole (2) and thiophene (7) using the larger 6-311++G(d,p) basis sets at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,p) and B3LYP/cc-pVTZ levels of theory gave little difference between calculated and experimental values of coupling constants. In general, the (1)H and 13C chemical shifts for all compounds are in good agreement with theoretical calculations using the smaller 6-31 basis set. The values of nJHH(n=3, 4, 5) and rmnJ(CH)(n=1, 2, 3, 4) were predicted well using the larger 6-31+G(d,p) and 6-311++G(d,p) basis sets and at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,2p) levels of theory. The computed atomic charges [Mülliken; Natural Bond Orbital Analysis (NBO); Merz-Kollman (MK); CHELP and CHELPG] for the B3LYP/6-311++G(d,p) geometry optimized structures of 1-17 were used to explore correlations with the experimental proton and carbon chemical shifts.     

Computational Study of Cage Like (ZnO)12 Cluster Using Hybrid and Hybrid Meta Functionals

Density Functional Theory employing hybrid and M06 functionals in combination with three different basis sets is used to calculate the ground state of a cage like (ZnO)₁₂ nanocluster which has been consistently reported as the more stable cluster for its particular size. B3LYP and B3PW91 hybrid functionals combined with 6‐31+G*, Lanl2dz and SDD basis sets are employed to treat the ZnO molecular system. Alternatively, three M06 functionals in combination with three basis sets are employed in the nanostructure calculations. Results obtained by treating ZnO sodalite cage nanocluster with M06 functionals demonstrated comparable quality to results obtained with hybrid functionals. Within this study, efficient theoretical DFT methods with the widely known hybrid and the recently created M06 meta‐hybrid functionals are employed to study nanostructured ZnO. Our resulting parameters provide a fresh approach performance wise on the different theoretical methods to treat transition metal nanostructures, particularly, ZnO nanoclusters geometry and electronic structure.     

Polarization functions for the modified m6‐31G basis sets for atoms Ga through Kr

The 2df polarization functions for the modified m6‐31G basis sets of the third‐row atoms Ga through Kr (Int J Quantum Chem, 2007, 107, 3028; Int J. Quantum Chem, 2009, 109, 1158) are proposed. The performances of the m6‐31G, m6‐31G(d,p), and m6‐31G(2df,p) basis sets were examined in molecular calculations carried out by the density functional theory (DFT) method with B3LYP hybrid functional, Møller‐Plesset perturbation theory of the second order (MP2), quadratic configuration interaction method with single and double substitutions and were compared with those for the known 6‐31G basis sets as well as with the other similar 641 and 6‐311G basis sets with and without polarization functions. Obtained results have shown that the performances of the m6‐31G, m6‐31G(d,p), and m6‐31G(2df,p) basis sets are better in comparison with the performances of the known 6‐31G, 6‐31G(d,p) and 6‐31G(2df,p) basis sets. These improvements are mainly reached due to better approximations of different electrons belonging to the different atomic shells in the modified basis sets. Applicability of the modified basis sets in thermochemical calculations is also discussed. © 2013 Wiley Periodicals, Inc.     

丁二酰亚胺的结构、振动频率和热力学性质计算

用密度泛函理论（ＤＦＴ）和从头计算（ａｂ ｉｎｉｔｉｏ）方法,在Ｂ３ＬＹＰ／６－３１Ｇ、Ｂ３ＬＹＰ／６－３１１Ｇ和ＭＰ２／６－３１１Ｇ水平上,全优化计算了了二酰亚胺的分子几何构型和电子结构．进行了简正振动频率分析并用校正后的频率计算了２００－６００Ｋ温度范围的标准热力学函数,对计算结果进行了比较和讨论．     

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。     

Electron momentum spectroscopy of CF2Cl2: experimental and theoretical momentum profiles for outer valence orbitals

Electron momentum distributions for outer valence orbitals of CF2Cl2 have been obtained by (e,2e) electron momentum spectroscopy at an incident energy of 1200 eV + binding energy. The experimental electron momentum profiles are compared with Hartree-Fock and density functional theory (DFT) calculations using B3LYP hybrid functional with the 6-31G and 6-311+G* basis sets. Generally, the shapes of the experimental momentum profiles are well reproduced by DFT calculations using larger basis sets 6-311 + G*. An attempt has been made to clarify the ordering of the outer valence orbitals, which have been in controversy, by comparing experimental results with B3LYP/6-311 + G* calculations.     

Density functional theory calculations of the lowest energy quintet and triplet states of model hemes: role of functional, basis set, and zero-point energy corrections

We investigated the effect of several computational variables, including the choice of the basis set, application of symmetry constraints, and zero-point energy (ZPE) corrections, on the structural parameters and predicted ground electronic state of model 5-coordinate hemes (iron(II) porphines axially coordinated by a single imidazole or 2-methylimidazole). We studied the performance of B3LYP and B3PW91 with eight Pople-style basis sets (up to 6-311+G*) and B97-1, OLYP, and TPSS functionals with 6-31G and 6-31G* basis sets. Only hybrid functionals B3LYP, B3PW91, and B97-1 reproduced the quintet ground state of the model hemes. With a given functional, the choice of the basis set caused up to 2.7 kcal/mol variation of the quintet-triplet electronic energy gap (DeltaEel), in several cases, resulting in the inversion of the sign of DeltaEel. Single-point energy calculations with triple-zeta basis sets of the Pople (up to 6-311G++(2d,2p)), Ahlrichs (TZVP and TZVPP), and Dunning (cc-pVTZ) families showed the same trend. The zero-point energy of the quintet state was approximately 1 kcal/mol lower than that of the triplet, and accounting for ZPE corrections was crucial for establishing the ground state if the electronic energy of the triplet state was approximately 1 kcal/mol less than that of the quintet. Within a given model chemistry, effects of symmetry constraints and of a "tense" structure of the iron porphine fragment coordinated to 2-methylimidazole on DeltaEel were limited to 0.3 kcal/mol. For both model hemes the best agreement with crystallographic structural data was achieved with small 6-31G and 6-31G* basis sets. Deviation of the computed frequency of the Fe-Im stretching mode from the experimental value with the basis set decreased in the order: nonaugmented basis sets, basis sets with polarization functions, and basis sets with polarization and diffuse functions. Contraction of Pople-style basis sets (double-zeta or triple-zeta) affected the results insignificantly for iron(II) porphyrin coordinated with imidazole. Poor performance of a "locally dense" basis set with a large number of basis functions on the Fe center was observed in calculation of quintet-triplet gaps. Our results lead to a series of suggestions for density functional theory calculations of quintet-triplet energy gaps in ferrohemes with a single axial imidazole; these suggestions are potentially applicable for other transition-metal complexes.     

戊烯自由基阳离子的密度泛函理论研究

使用密度泛函理论B3LYP方法和6-31G(d,p)、6-31＋G(d,p)、6-311G(d,p)及6-311＋G(d,p)基组，分别对2-C5H10＋和1-C5H10＋的各种构象进行了几何构型优化，并用B3LYP/6-311G(d,p)进行了频率分析计算.计算预言1-C5H10＋具有非平面构型，与以往报导的从头算计算结论相反.在两个自由基阳离子的各种构象的B3LYP几何构型上，进行了B3LYP和UMP2(full)方法的超精细偶合常数计算，得到了比以往更好的结果.     

Peculiar basis set dependence of the energetics of C2S2H2 isomers. In search of adequate and affordable basis set for routine calculations

Quantum mechanical calculations using the Hartree-Fock (HF), post-Hartree-Fock {MP2 and CCSD(T)}and gradient-corrected hybrid density functional variant, B3LYP methodology in conjugation with basis sets like 6-31G*, 6-311G** and cc-pVTZ, were employed to critically probe the right quality of basis set and the appropriate level of theory that can be applied in modeling the organo-sulfur compounds. The relative stability ordering of 1,2-dithiete and dithioglyoxal reveal the delicate basis set dependence especially on ‘S’ atom. Single point calculations at the B3LYP, MP2 and CCSD(T) levels using a series of basis set ranging from double ζ quality all the way up to the quintuple ζ quality were done to illustrate the effect of electron correlation and the basis set dependency for these compounds. Basis set requirements are much higher than affordable for medium sized molecules as very slow convergence is seen even when the calculations are carried out with basis set as high as cc-pV5Z at the B3LYP and MP2 level of theories.     

Density functional efficiency in the calculations of vibrational frequencies and molecular structures of β-diketones

Density functional theory (DFT) levels are employed to calculate the vibrational frequencies and geometrical data of β-diketones. We evaluate the relative performance of the different levels by comparing theoretical results to experimental values. The applied DFT levels in this work are B3LYP, BLYP, B3P86, B3PW91, BPW91, G96LYP, BP86, and G96PW91 with the standard 6-31G, 6-31G*, 6-31G**, 6-31+G**, 6-31++G**, 6-311G**, 6-311++G** basis sets. The best results are obtained at the B3LYP, B3PW91, and B3P86 levels.     

Crystal structure and theoretical calculations of Julocrotine,a natural product with antileishmanial activity

Julocrotine, N‐(2,6‐dioxo‐1‐phenethyl‐piperidin‐3‐yl)‐2‐methyl‐butyramide, is a potent antiproliferative agent against the promastigote and amastigote forms of Leishmania amazonensis (L.). In this work, the crystal structure of Julocrotine was solved by X‐ray diffraction, and its geometrical parameters were compared with theoretical calculations at the B3LYP and HF level of theory. IR and NMR spectra also have been obtained and compared with theoretical calculations. IR absorptions calculated with the B3LYP level of theory employed together with the 6‐311G+(d,p) basis set, are close to those observed experimentally. Theoretical NMR calculations show little deviation from experimental results. The results show that the theory is in accordance with the experimental data. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

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.     

吡啶-BH~3相互作用复合物的理论研究

对吡啶-BH~3复合物分别用MP2/6-31+G^*和B3LYP/6-31+G^*进行理论计算以预测该复合物的构型及解离能，得到四种构型，在MP2优化构型基础上作CCSD/6-31+G^*单点能量计算以验证MP2与B3LYP结果的可靠性，然后用B3LYP作振动频率分析，计算了各构型的垂直电离势，最后用更大基组作单点能量计算和自然键轨道(NBO)分析。结果表明，N-B直接相连的构型最稳定，其解离能为141.50kJ/mol,MP2和B3LYP对N-H接近的构型结果相关较大，另外两种构型稳定性介于二者之间，解离能分别为15.18kJ/mol,14.06kJ/mol(MP2/6-31+G^*)。     

Probing furanose ring conformation by gas-phase computational methods: energy profile and structural parameters in methyl beta-D-arabinofuranoside as a function of ring conformation

The potential energy surface of methyl beta-D-arabinofuranoside (3) has been studied by ab initio molecular orbital (HF/6-31G) and density functional theory (B3LYP/6-31G) calculations via minimization of the 10 possible envelope conformers. The partial potential energy surface identified that the global minimum and lowest energy northern conformer was E(2). In the HF calculations, (2)E was the most stable southern conformer, while the density functional theory methods identified (4)E as the local minimum in this hemisphere. Additional calculations at higher levels of theory showed that the B3LYP-derived energies of many of the envelope conformers of 3 are dependent upon the basis set used. It has also been demonstrated that B3LYP/6-31+G//B3LYP/6-31G single point energies are essentially the same as those obtained from full geometry optimizations at the B3LYP/6-31+G level. The northern and southern minima of the B3LYP/6-31+G surface are, respectively, the E(2) and (2)E conformers. The B3LYP/6-31G geometries were used to study the relationship between ring conformation and various structural parameters including bond angles, dihedral angles, bond lengths, and interatomic distances.