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.     

DFT study of the structural characteristics of the yttrium(3+) aqua ion

Density functional theory (DFT) using SVWN5, B3LYP, B3P86, O3LYP, B3PW91, B1LYP, B971, MPW1PW91, PBE1PBE, BHandH, and BHandHLYP density functionals was employed to study the structural characteristics of the Y(H₂O) ₈ ³⁺ yttrium aqua ion. The nonlocal hybrid GGA functionals show worse predictive ability in structural calculations of the Y(H₂O) ₈ ³⁺ aqua ion compared to the relatively simple combined functional BHandH and to the simplest SVWN5 functional in LSDA theory.     

一些密度泛函方法预测电子亲和势

选取了杂化泛函B3LYP, B3PW91, O3LYP, PBE0, 以及与之相对应的GGA泛函BLYP, BPW91, OLYP和PBE, 还选取了能更好地兼顾强相互作用和弱相互作用的X3LYP泛函和在预测NMR的化学位移有较好表现的OPBE泛函, 以及两种meta-GGA泛函VSXC和TPSS, 共12种泛函, 详细地考察了这些泛函在预测EA方面的准确性.     

Determination of the absolute configuration of chiral molecules via density functional theory calculations of vibrational circular dichroism and optical rotation: The chiral alkane D3-anti-trans-anti-trans-anti-trans-perhydrotriphenylene

The Absolute configuration (AC) of the chiral alkane D₃-anti-trans-anti-trans-anti-trans-perhydrotriphenylene (PHTP), 1, is determined by comparison of density functional theory (DFT) calculations of its vibrational circular dichroism (VCD) and optical rotation (OR) to the experimental VCD and OR of (+)−1, obtained in high enantiomeric excess using chiral gas chromatography. Conformational analysis of 1 demonstrates that the all-chair (CCCC) conformation is the lowest in energy and that other conformations are too high in energy to be significantly populated at room temperature. The B3PW91/TZ2P calculated IR spectrum of the CCCC conformation of 1 is in excellent agreement with the experimental IR spectrum, confirming the conformational analysis and demonstrating the excellent accuracy of the B3PW91 functional and the TZ2P basis set. The B3PW91/TZ2P calculated VCD spectrum of the CCCC conformation of S-1 is in excellent agreement with the experimental VCD spectrum of (+)−1, unambiguously defining the AC of 1 to be S(+)/R(−). The B3LYP/aug-cc-pVDZ calculated OR of S-1 over the range 589–365 nm has the same sign and dispersion as the experimental OR of (+)−1, further supporting the AC S(+)/R(−). Our results confirm the AC proposed earlier by Farina and Audisio. This study provides a further demonstration of the excellent accuracy of VCD spectra predicted using Stephens’ equation for vibrational rotational strengths together with the ab initio DFT methodology, and further documents the utility of VCD spectroscopy in determining the ACs of chiral molecules.     

Vibrational circular dichroism and absolute configuration of chiral sulfoxides: tert-butyl methyl sulfoxide

Mid-infrared vibrational unpolarised absorption and vibrational circular dichroism (VCD) spectra of CCl4 solutions of tert-butyl methyl sulfoxide (1) are reported. The spectra are compared to ab initio density functional theory (DFT) calculations carried out using two functionals, B3PW91 and B3LYP, and two basis sets, 6-31G* and TZ2P. The VCD spectra are calculated using Gauge-invariant atomic orbitals (GIAOs). The analysis of the VCD spectrum confirms the R(-)/S(+) absolute configuration of 1. The advantages and disadvantages of VCD spectroscopy in determining the absolute configurations of chiral sulfoxides are discussed.     

On the accuracy of density-functional theory exchange-correlation functionals for H bonds in small water clusters: benchmarks approaching the complete basis set limit

The ability of several density-functional theory (DFT) exchange-correlation functionals to describe hydrogen bonds in small water clusters (dimer to pentamer) in their global minimum energy structures is evaluated with reference to second order Moller-Plesset perturbation theory (MP2). Errors from basis set incompleteness have been minimized in both the MP2 reference data and the DFT calculations, thus enabling a consistent systematic evaluation of the true performance of the tested functionals. Among all the functionals considered, the hybrid X3LYP and PBE0 functionals offer the best performance and among the nonhybrid generalized gradient approximation functionals, mPWLYP and PBE1W perform best. The popular BLYP and B3LYP functionals consistently underbind and PBE and PW91 display rather variable performance with cluster size.     

Structures and excitation energies of Zn–tetraarylporphyrin analogues: A theoretical study

The photophysical properties of β-substituted Zn–tetraarylporphyrin (ZnTAP) analogues used as dyes in dye-sensitized solar cells were studied using density functional theory (DFT). Singlet-excitation energy calculations of ZnTAP analogues were performed using time-dependent DFT with B3LYP, B3PW91, PBE0 exchange–correlation functionals at 6-31G(d) and 6-31+G(d) basis sets using B3LYP/6-31G(d) geometries. The PBE0 functional at 6-31+G(d) basis set provided a better correlation with the experimental data for both B- and Q-bands. The inclusion of solvation effect in the calculations provided a good agreement in terms of B:Q_ave ratio of the oscillator strengths for both analogues with the experimental values. Analogue 2 has a higher and a more balanced charge-carrier transport rates than analogue 1. In general, the addition of an electron-donating group in the meso-substituent (analogue 2) resulted in a narrower band gap, higher oscillator strength, a more red-shifted absorption spectra, and better charge-transfer characteristics than analogue 1.     

Electronic structures of 4d transition metal monoxides by density functional theory

Bond distances, dissociation energies, ionization potentials and electron affinities of 4d transition metal monoxides from YO to CdO and their positive and negative ions were studied by use of density functional methods B3LYP, BLYP, B3PW91, BPW91, B3P86, BP86, SVWN, MPW1PW91 and PBE1PBE. It was found that calculated properties are highly dependent on the functionals employed, especially for dissociation energy. For most neutral species, pure density functionals BLYP, BPW91 and BP86 have good performance in predicting dissociation energy than hybrid density functionals B3LYP, B3PW91 and B3P86. In addition, BLYP gives the largest bond distance compared with other density functional methods, while SVWN gives shortest bond distance, largest dissociation energy and electron affinity. For the ground state, the spin multiplicity of the charged species can be obtained by ± 1 of their corresponding neutral species.     

The confirmation of accurate combination of functional and basis set for transition‐metal dimers: Fe2, Co2, Ni2, Ru2, Rh2, Pd2, Os2, Ir2, and Pt2

Eight kinds of density functionals named B3LYP, PBE1PBE, B1B95, BLYP, BP86, G96PW91, mPWPW91, and SVWN along with two different valence basis sets (LANL2DZ and CEP‐121g) are employed to study the transition‐metal dimers for the elements of group VIII. By comparing the equilibrium bond distances, vibrational frequencies, and dissociation energies of the ground state of these dimers with the available experimental values and theoretical data, we show that the “pure” DFT methods (G96PW91, BLYP, and BP86) with great‐gradient approximation always give better results relative to the hybrid HF/DFT schemes (B3LYP, PBE1PBE, and B1B95). The striking case found by us is that the G96PW91 functional, which is not tested in previous systemic studies, always predicts the dissociation energy to be well. The Ru₂ and Os₂ dimers are sensitive to not only the functionals employed but also the valence basis sets adopted. The natural bond orbital population is analyzed, and the molecular orbitals of the unpaired electrons are determined. Furthermore, our results indicate that the s and d orbitals of these dimers always hybridize with each other except for Rh₂ and Pt₂ molecules. And by analyzing the electron configuration of the bonding atom, the dissociation limit of the ground state is obtained. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Stable alkanes containing very long carbon-carbon bonds

The metal-induced coupling of tertiary diamondoid bromides gave highly sterically congested hydrocarbon (hetero)dimers with exceptionally long central C-C bonds of up to 1.71 ? in 2-(1-diamantyl)[121]tetramantane. Yet, these dimers are thermally very stable even at temperatures above 200 °C, which is not in line with common C-C bond length versus bond strengths correlations. We suggest that the extraordinary stabilization arises from numerous intramolecular van der Waals attractions between the neighboring H-terminated diamond-like surfaces. The C-C bond rotational dynamics of 1-(1-adamantyl)diamantane, 1-(1-diamantyl)diamantane, 2-(1-adamantyl)triamantane, 2-(1-diamantyl)triamantane, and 2-(1-diamantyl)[121]tetramantane were studied through variable-temperature (1)H- and (13)C NMR spectroscopies. The shapes of the inward (endo) CH surfaces determine the dynamic behavior, changing the central C-C bond rotation barriers from 7 to 33 kcal mol(-1). We probe the ability of popular density functional theory (DFT) approaches (including BLYP, B3LYP, B98, B3LYP-Dn, B97D, B3PW91, BHandHLYP, B3P86, PBE1PBE, wB97XD, and M06-2X) with 6-31G(d,p) and cc-pVDZ basis sets to describe such an unusual bonding situation. Only functionals accounting for dispersion are able to reproduce the experimental geometries, while most DFT functionals are able to reproduce the experimental rotational barriers due to error cancellations. Computations on larger diamondoids reveal that the interplay between the shapes and the sizes of the CH surfaces may even allow the preparation of open-shell alkyl radical dimers (and possibly polymers) that are strongly held together exclusively by dispersion forces.     

Density functional theoretical (DFT) study for the prediction of spectroscopic parameters of ClCCCN

DFT(B3LYP, B3PW91) calculations in conjunction with three different basis sets have been utilized to investigate the variations in the bond lengths, dipole moment, rotational constants, IR frequencies, IR intensities and rotational invariants of ClCCCN. The nuclear quadrupole constants of chlorine ((35)Cl, (37)Cl) and nitrogen ((14)N) of ClCCCN have been calculated on the experimental r(s) structure as well as on the B3PW91/6-311++g(d,p) optimized geometry and were found to be within the scale length of the experimental uncertainty. The slope and intercept obtained from the regression analysis between the B3LYP/6-311++g(d,p) level calculated and experimental B(o) values of ClCCCN were used to calculate reasonable values of rotational constants of all the rare isotopic species of ClCCCN having standard deviation +/-0.048 MHz. All the spectroscopic parameters obtained from DFT calculations show satisfactory agreement with the available experimental data.     

Systematic studies on the computation of nuclear magnetic resonance shielding constants and chemical shifts: the density functional models

We present a systematic density functional investigation on the prediction of the 13C, 15N, 17O, and 19F NMR properties of 23 molecules with 21 density functionals. Extensive comparisons are made for both 13C magnetic shieldings and chemical shifts with respect to the gas phase experimental data and the best CCSD(T) results. We find that the OPBE and OPW91 exchange-correlation functionals perform significantly better than some popular functionals such as B3LYP and PBE1PBE, even surpassing, in many cases, the standard wavefunction-based method MP2. Further analysis has been performed to explore the individual role played by various exchange and correlation functionals. We find that the B88 and PBE exchange functionals have a too strong tendency of deshielding, leading to too deshielded magnetic shielding constants; whereas the OPTX exchange functional performs remarkably well. We claim that the main source of error arises from the exchange functional, but correlation functional also makes important contribution. We find that the correlation functionals may be grouped into two classes. class A, such as LYP and B98, leads to deshielded NMR values, deteriorating the overall performance; whereas class B, such as PW91 and PBE, generally increases the absolute shieldings, which complements the exchange functionals, leading to improved results in the calculation of NMR data.     

Calculated gas-phase infrared spectra of 2,2,5,5,8,8-hexamethylhexahydroimidazo [1,2-a]-pyrazine-3,6-dione: relative performance of Hartree-Fock and hybrid density functional theory methods.

Geometric parameters and IR spectra of 2,2,5,5,8,8-hexamethylhexahydroimidazo[1,2-a]pyrazine-3,6-dione were computed by the HF, B3LYP, B3P86 and B3PW91 methods with the 6-31G(d) basis set. All the computation methods produce a boat conformation of the six-membered ring with the orientation opposite to the one experimentally observed, that is obviously due to incapability of such calculations to take into account mutual influence of the molecules in a crystal package. Quality of predicting the interatomic distances observed experimentally decreases in the series HF, B3LYP, B3PW91 and B3P86; for bond angles, in the series B3LYP, P3PW91, B3P86 and HF. At the same time, the IR spectra computed are in a good agreement with the observed FTIR spectrum. The correlation between the calculated and experimental vibration frequencies is characterized by the coefficients higher than 0.9999 for all three DFT methods; for HF it is slightly lower than 0.9995. The calculated absolute band intensities satisfactory match the observed relative intensities as well. Optimal uniform scaling factors calculated are 0.8973, 0.9593, 0.9540 and 0.9552 for HF, B3LYP, B3P86 and B3PW91, respectively.     

Molecular structure and vibrational investigation of benzenesulfonic acid methyl ester using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) theory calculations

The FT-Raman and FT-IR spectra for benzenesulfonic acid methyl ester (BSAME) have been recorded in the region 4000-100 cm(-1) and compared with the harmonic vibrational frequencies calculated using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) method by employing 6-311G (d, p) basis set with appropriate scale factors. IR intensities and Raman activities are also calculated by DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) methods. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values for sulfonic acid and some substituted sulfonic acids. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction from DFT. The scaled vibrational frequencies at LSDA/B3LYP/6-311G (d, p) seem to coincide with the experimentally observed values with acceptable deviations. The theoretical spectrograms (IR and Raman) have been constructed and compared with the experimental FT-IR and FT-Raman spectra. Some of the vibrational frequencies of the sulfonic acid are effected upon profusely with the methyl substitution in comparison to benzene sulfonamide and these differences are interpreted.     

Comparison of DFT methods for molecular structure and vibration spectra of ofloxacin calculations

Comparison of the performance of different density functional theory (DFT) methods at various basis sets in predicting molecular and vibration spectra of ofloxacin was reported. The methods employed in this study comprise six functionals, namely, mPW1PW91, HCTH, LSDA, PBEPBE, B3PW91 and B3LYP. Different basis sets including LANL2DZ, SDD, LANL2MB, 6-31g, 6-311g and 3-21g were also examined. Comparison between the calculated and experimental data indicates that the mPW1PW91/6-311g level afford the best quality to predict the structure of ofloxacin. The results also indicate that B3LYP/LANL2DZ level show better performance in the vibration spectra prediction of ofloxacin than other DFT methods.     

Density functional study of AuXq (X = O, S, Se, Te, q = +1, 0, -1) molecules

Bond distances, vibrational frequencies, electron affinity, ionization potential, and dissociation energies of the title molecules were studied by use of density functional methods B3LYP, B3P86, B3PW91, BHLYP, BLYP, BP86, mPW1PW91, and PBE1PBE. It was found that the ground electronic state is doublet for neutral species, singlet for the anion, and triplet for the cation, in agreement with experiments and previous theoretical studies. The calculated properties are highly dependent on the functionals employed, in particular for the dissociation energy. The predicted bond distances and vibrational frequencies are in agreement with experiments and previous theoretical results. BP86 and BLYP have relatively good performance in reproducing the experimental results, while BHLYP is the worst functional method compared with the other density functional methods used for the title molecules.