CAM-B3LYP Functionals Research Articles

Computational methodology study of the optical and thermochemical properties of a molecular photoswitch.

We assess how the utilization of different DFT functionals for obtaining the equilibrium geometries and vibrational frequencies affect the description of the thermochemistry and subsequent calculation of the optical properties of a dihydroazulene-vinylheptafulvene photoswitch. The assessment covers nine popular DFT functionals (BLYP, B3LYP, CAM-B3LYP, M06-L, M06, M06-2X, PBE, PBE0, and ωB97X-D) in conjugation with five different Pople style basis sets (6-31+G(d), 6-31++G(d,p), 6-311+G(d), 6-311++G(d,p), and 6-311++G(3df,3pd)). It is identified that only CAM-B3LYP, M06-2X, and PBE0 are able to quantitatively describe the correct trends in the thermochemical properties. The subsequent calculation of the optical properties using the CAM-B3LYP functional shows that there is little difference in whether the CAM-B3LYP, M06-2X, or PBE0 functionals have been used to calculate the equilibrium geometries. Utilizing the identified functionals, we investigate how the number of electron withdrawing cyano substituents influence the thermochemistry and optical properties of the molecular photoswitch.

Performance of Twelve Density Functional Theory Methods in the Characterization of Three Trivalent Uranium Complexes

We report a comparative study on the characterization of three trivalent uranium complexes using 12 density functional theory (DFT) methods, i.e., BP86, PBE, B3LYP, B3PW91, BHandHLYP, PBE0, X3LYP, CAM-B3LYP, TPSS, M06L, M06, and M06-2X, representing (meta-)GGA and hybrid (meta-)GGA levels of treatment of molecular systems. The MP2 method was used in single-point calculations to provide an ab initio view of the electronic structure. Three model systems in the experimental work on the activation of CO2 and CS2 by a trivalent uranium complex (Tp*)(2)U-eta(1)-CH2Ph (Cpd2) were used i.e., (Tp*)(2)U-eta(1)-CH2Ph (Cpd2), (Tp*)(2)U-kappa(2)-O2CCH2Ph (Cpd3), and (Tp*)(2)U-kappa(2)-S2CCH2Ph (Cpd4) (Tp=hydrotris(3,5-dimethylpyrazolyl)borate). The hybrid functionals, B3LYP and B3PW91, displayed good performance in view of both the geometrical and electronic structures. The MP2 method generated consistent results as OFT methods for Cpd2 and Cpd3, while provided an odd picture of the electronic structure of Cpd4 that may be due to its single determinant feature, leading to its capture of an electronic configuration of Cpd4 different from the one with the DFT methods. The use of a quasi-relativistic 5f-in-core ECP (LPP) treatment for U(III) in the thermodynamic calculations was supported by the calculations with a small-core ECP treatment (SPP) for U. Owing to increasing interests in low-valent actinide molecular systems, this work complements previous comparative studies, which mainly focus on high-valent actinide complexes, and provides timely information on the performance of 12 widely used DFT methods in studying low-valent actinide systems. It is expected to contribute to a more sensible selection of DFT methods in the study of low-valent actinide molecular systems.

Properties of noncovalent tetraphenylporphine···C60 dyads as studied by different long-range and dispersion-corrected DFT functionals.

The noncovalent dyad of tetraphenylporphine and C60 fullerene (H2TPP···C60) and the tetraphenylporphine dimer (H2TPP···H2TPP) were studied by density functional theory (DFT), using functionals that incorporate empirical dispersion correction (DFT-D), functionals that use a long-range correction (LC) scheme, a hybrid functional (B3LYP) and a highly parametrized empirical exchange-correlation functional (M05-2X). The results were compared to X-ray structures and interaction energies reported in previous experimental and theoretical studies. It was found that B3LYP and CAM-B3LYP functionals fail to reproduce the X-ray structures and binding energies of the TPP···C60 system. DFT-D functionals overestimated the π···π energy interactions for both systems, however, the optimized structures agree well with those observed experimentally. The LC-BLYP functional predicts geometries similar to X-ray structures; nevertheless, due to the lack of correction in the dispersion energy, the predicted energies for both model systems are low. On the other hand, the M05-2X functional exhibited the best performance. Both the structures and binding energies calculated with M05-2X are consistent with experimental and theoretical evidence reported by other authors, as well as with our experimental results obtained by means of atomic force microscopy on H2TPP thin films grown on the HOPG/C60 substrate by physical vapor deposition.

TDDFT assessment of functionals for optical 0-0 transitions in small radicals.

Using LR-TDDFT, we calculated the 0-0 energies of 15 small radicals for which the experimental values in gas phase are available. We used 17 functionals. It turned out that B3LYP, M06-2X, ωB97X-D, CAM-B3LYP, and HSE06 functionals are the most effective functionals in terms of root-mean-square and average unsigned deviation. Using the standard value (0.47 a0(-1)) of the attenuation parameter ω, the long-range-corrected LC-GGA functionals give poor results. However, the LC-PBE with ω = 0.25 a0(-1) give a performance similar to that of B3LYP. Taking into account zero-point correction improves the results, but the contribution of adiabatic correction is more important than that due to the vibration. The vertical approximation is certainly not recommended. An adiabatic calculation seems to give a good compromise between computing time (and resources) and reliability of the results for most of molecules investigated in this work.

The structure and UV spectroscopy of benzene-water (Bz-W6) clusters using time-dependent density functional theory.

DFT and MP2 calculations are performed to obtain optimized ground state geometries and binding energies of the cage and the prism conformers of water W6 clusters and Bz-W6 clusters using the aug-cc-pVDZ basis set. The cage conformer of Bz-W6 system is found to be more stable than prism conformer for all range of DFT functionals and MP2. Time dependent-DFT is then used to study UV spectroscopy of Bz, water W6 clusters and Bz-W6 clusters at both the MP2 and wB97XD optimized ground state geometries using the B3LYP, CAM-B3LYP and M06-2X functionals with 6-31++G(d,p) and aug-cc-pVTZ basis sets. Our results predict minor differences in the UV spectroscopy of cage and prism conformers W6 and Bz-W6 clusters that may be observable with high-resolution spectroscopy. The M06-2X and CAM-B3LYP functionals perform consistently with each other. Benzene-mediated excitations of the water W6 cluster towards longer wavelengths above 170 nm are noticed in both the cage and prism geometries of Bz-W6. Benzene is found to be influenced after interacting with the cage and prism W6 geometries, and is seen to undergo a red shift in the main π→π* electronic transition, in which the degeneracy is slightly broken. Charge transfer (CT) states and diffuse Rydberg-type states are also found to play an important role in the spectroscopy of such systems.

Identification of structural and spectral properties of synthesized 3-(p-isopropylphenyl)-5-(o,m,p-nitrophenyl)-1-phenylformazans: A combined experimental and DFT study

The fomazan compounds 3-(p-isopropylphenyl)-5-(o,m,p-nitrophenyl)-5-phenylformazans (1–3) have been synthesized and characterized by FTIR, UV–Vis and 1H NMR spectroscopic techniques and elemental analysis. Quantum chemical calculations of the molecular structures, vibrational frequencies, gauge including atomic orbital 1H chemical shift values were carried out using the density functional B3LYP method with the 6-311 + G(d,p) basis set. The TD-DFT calculations were carried out using the B3LYP, CAM-B3LYP and PBE1PBE functionals with the 6-311 + G(d,p) basis set to determine the maximum absorbtion wavelength of the UV–Vis spectra for (1–3). The non-linear optical properties are addressed theoretically. Besides, DFT calculations of the molecular electrostatic potential, the natural bond orbital and thermodynamic properties of (1–3) were carried out at the B3LYP/6–311 + G(d,p) level of theory.

An experimental and density functional study on conformational and spectroscopic analysis of 5-methoxyindole-2-carboxylic acid

In this article, a brief conformational and spectroscopic characterization of 5-methoxyindole-2-carboxylic acid (5-MeOICA) via experimental techniques and applications of quantum chemical methods is presented. The conformational analysis of the studied molecule was determined theoretically using density functional computations for ground state, and compared with previously reported experimental findings. The vibrational transitions were examined by measured FT-IR and FT-Raman spectroscopic data, and also results obtained from B3LYP and CAM-B3LYP functionals in combination with 6-311++G(d,p) basis set. The recorded proton and carbon NMR spectra in DMSO solution were analyzed to obtain the exact conformation. Due to intermolecular hydrogen bondings, NMR calculations were performed for the dimeric form of 5-MeOICA and so chemical shifts of those protons were predicted more accurately. Finally, electronic properties of steady compound were identified by a comparative study of UV absorption spectra in ethanol and water solution and TD-DFT calculations.

Theoretical study on absorption and emission spectra of pyrrolo-C analogues

Fluorescent nucleoside analogues have attracted much attention in studying the structure and dynamics of nucleic acids in recent years. In the present work, we use theoretical calculations to investigate the structural and optical properties of Pyrrolo-C (PyC) and its analogues which are modified via the conjugation or fusion of different aromatic ring to the PyC core. We also consider the effects of aqueous solution and base pairing. The results show that the fluorescent pyrrolo-C analogues can pair with guanosine to form stable H-bonded WC base pairs. The calculated absorption peaks of modified deoxyribonucleosides agree well with the measured data. The absorption and emission maxima of the pyrrolo-C analogues are greatly red shifted compared with nature C. The solvent effects can induce wavelength blue shift and increase the oscillator strengths in both the absorption and emission spectra. With regard to the WC base pairs, the B3LYP functional reveals that the lowest energy transitions of modified GC base pairs are charge transfer excitation while the CAM-B3LYP functional predicts that all the lowest transitions are localised on the pyrrolo-C analogues. The M062X and CAM-B3LYP functionals show good agreement with respect to both the value of the lowest energy transitions as well as the oscillator strengths.

DFT and TD-DFT studies on osmacycle dyes with tunable photoelectronic properties for solar cells

B3LYP and CAM-B3LYP functionals have been used to determine structures, electronic and optical properties of osmium-bridged tricyclic aromatic compounds. Calculations show that the optical properties and charge separation features of these osmacycle derivatives can be well modified by incorporating different π-bridge groups. In particular, the newly designed osmacycle dyes 5 and 6 by embedding thiophene and thienothiophene bridge units to osmium polycyclic aromatic system show very strong and broad adsorptions in the whole visible region and excellent charge separation in the first excited state of 1(ππ*) from the hightest occupied molecular orbital to the lowest unoccupied molecular orbital excitation. Furthermore, the predicted relatively high light harvesting efficiency and large driving force for electron injection suggest that they are quite promising for design of high-performance dye-sensitized solar cells.

Polarizabilities from Long-Range Corrected DFT Calculations

The long-range corrected DFT functionals, LC-BLYP, LC-PBE and CAM-B3LYP with the augmented Dunning-type triple-ζ basis sets represent dynamical polarizabilities at λ = 589.3 nm of 105 medium-sized organic compounds containing C, H, O, N, S, P, F, Cl, Br and I elements with the root mean squared deviations (RMSD) of about 0.34, 0.35, and 0.42 Å3, respectively. These errors do not change appreciably when the augmented double-ζ basis sets are used. The functionals with 100% of Hartree–Fock (HF) exchange at long-range perform best for aromatic compounds and the CAM-B3LYP or B3LYP functionals for fully saturated compounds. The degrees of HF exchange in mid- and long-range affect strongly the shape and location of the distributions of absolute errors in polarizability, P(Δα). The differences between functionals belonging to the BLYP and PBE families, and having the same degree of HF exchange, have much smaller effect on the P(Δα) distributions.

Synthesis and photophysical properties of two-photon chromophores containing 1H-benzimidazole residue

The non-centrosymmetric, trans,trans-2-{4-[2-(1H-benzimidazol-2-yl)ethenyl]-styryl}-1,3-dimethylbenzimidazole iodide and centrosymmetric, trans,trans-1,4-bis[4-(2-(1H-benzimidazol-2-yl)ethenyl)]benzene polymethine compounds based on 1H-benzimidazole residue were synthesized and characterized. Their photophysical properties in solvents of different polarity were thoroughly studied by means of absorption, emission and fluorescence quantum yield measurements. Analysis of the results clearly indicates that the compounds have strong one-photon absorption bands in the near ultraviolet region, relatively high fluorescence quantum yields and large Stokes' shifts due to the charge transfer effect.The one- and two-photon absorption properties of a selected non-centrosymmetric dye were compared to those of a centrosymmetric polymethine dye. Their two-photon absorption cross-sections in DMF were determined to be ∼330 GM and ∼380 GM at ca. 650 nm for the centrosymmetric and non-centrosymmetric polymethine compounds, respectively.Density functional theory calculations of one- and two-photon absorption electronic spectra of the tested compounds using CAM-B3LYP, LC-BLYP and LC-ωPBE functionals were carried out to support the experimental data.

Structure and absorption of Co(III) azo complex dyes based on pyrrolinone esters: DFT and TD DFT study

The relation between structure and absorption of three symmetrical 2:1 octahedral Co(III) azo complexes was studied. Quantum chemical calculations based on density functional theory (DFT) relate well with E-azo configuration of ligands with coordinated nitrogen atoms coming solely from phenolic residues. DFT calculations estimate the mer stereoisomer as remarkably preferred with respect to any fac arrangement. Time dependent DFT calculations using B3LYP and CAM-B3LYP functionals were successfully used to interpret the absorption spectra in a visible range.

Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine.

Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-½) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by the long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localized spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.

Relative Stability of the La and Lb Excited States in Adenine and Guanine: Direct Evidence from TD-DFT Calculations of MCD Spectra.

The relative position of La and Lb ππ* electronic states in purine nucleobases is a much debated topic, since it can strongly affect our understanding of their photoexcited dynamics. To assess this point, we calculated the absorption and magnetic circular dichroism (MCD) spectra of adenine, guanine, and their nucleosides in gas-phase and aqueous solution, exploiting recent developments in MCD computational technology within time-dependent density functional theory. MCD spectroscopy allows us to resolve the intense S0→ La transition from the weak S0→ Lb transition. The spectra obtained in water solution, by using B3LYP and CAM-B3LYP functionals and describing solvent effect by cluster models and by the polarizable continuum model (PCM), are in very good agreement with the experimental counterparts, thus providing direct and unambiguous evidence that the energy ordering predicted by TD-DFT, La < Lb, is the correct one.

Analysis of nonlinear optical properties in donor-acceptor materials.

Time-dependent density functional theory has been used to calculate nonlinear optical (NLO) properties, including the first and second hyperpolarizabilities as well as the two-photon absorption cross-section, for the donor-acceptor molecules p-nitroaniline and dimethylamino nitrostilbene, and for respective materials attached to a gold dimer. The CAMB3LYP, B3LYP, PBE0, and PBE exchange-correlation functionals all had fair but variable performance when compared to higher-level theory and to experiment. The CAMB3LYP functional had the best performance on these compounds of the functionals tested. However, our comprehensive analysis has shown that quantitative prediction of hyperpolarizabilities is still a challenge, hampered by inadequate functionals, basis sets, and solvation models, requiring further experimental characterization. Attachment of the Au2S group to molecules already known for their relatively large NLO properties was found to further enhance the response. While our calculations show a modest enhancement for the first hyperpolarizability, the enhancement of the second hyperpolarizability is predicted to be more than an order of magnitude.

Quantum chemical perspective of efficient NLO materials based on dipolar trans-tetraammineruthenium (II) complexes with pyridinium and thiocyanate ligands: First theoretical framework

In this research work non-linear optical (NLO) properties of dipolar trans-tetraammineruthenium (II) complexes with pyridinium and thiocyanate ligands have been calculated by using density functional theory (DFT). For reference systems, four functionals B3LYP, PBE0, BHandHLYP and CAM-B3LYP were employed to select the best functional to study designed compounds on the basis of similarity between calculated and experimental results. The calculated static hyperpolarizabilities were found to be strongly functional dependent. The results from CAM-B3LYP seem to be more reliable when compared to the available experimental data. Thus, new compounds have been theoretically designed by the substitution of electron withdrawing atom/groups as acceptor on reference systems. All the designed compounds display intense band due to metal-to-ligand charge transfer (MLCT). The second-order polarizability has shown a remarkable increase on substitution of strong electron withdrawing atom/groups as an acceptor. The second-order polarizability of all the designed systems was high calculated to be 185×10−30 to 842×10−30esu.

Assessment of density-functionals for describing the X(-) + CH3ONO2 gas-phase reactions with X = F, OH, CH2CN.

The energetics of the ECO2, SN2@C and SN2@N channels of X(-) + CH3ONO2 (X = F, OH, CH2CN) gas-phase reactions were computed using the CCSD(T)/CBS method. This benchmark extends a previous study with X = OH [M. A. F. de Souza et al., J. Am. Chem. Soc., 2012, 134, 19004] and was used to ascertain the accuracy and robustness of nineteen density-functionals for describing these potential energy profiles (PEP) as well as the kinetic product distributions obtained from RRKM calculations. Assessments were based on the mean unsigned error (MUE), the mean signed error (MSE), the #best : #worst (BW) criterion and the statistical confidence interval (CI) for the MSE. In general, double-hybrid (DH) functionals perform better than the range-separated ones, and both are better than the global-hybrid functionals. Based on the MUE and CI criteria the B2GPPLYP, B2PLYP, M08-SO, BMK, ωB97X-D, CAM-B3LYP, M06, M08-HX, ωB97X and B97-K functionals show the best performance in the description of these PEPs. Within this set, the B2GPPLYP functional is the most accurate and robust. The RRKM results indicate that the DHs are the best for describing the selectivities of these reactions. Compared to CCSD(T), the B2PLYP method has a relative error of only ca. 1% for the selectivity and the accuracy to provide the correct conclusion concerning the nonstatistical behavior of these reactions.

Time-dependent density functional study of UV-visible absorption spectra of small noble metal clusters (Cun, Agn, Aun, n = 2–9, 20)

The absorption UV-visible spectra of noble metal clusters Cun, Agn, Aun, n = 2–9 and 20 are investigated in the framework of the time-dependent density functional theory using the long-range corrected density functionals LC-M06L and CAM-B3LYP and high-quality Gaussian basis sets. Some calculations including the spin–orbit coupling are also presented. The contribution of the d electrons to the optical response was found to be lower than it was when a purely local exchange functional was used. Calculated spectra are compared with experimental ones for clusters embedded in a rare-gas matrix.

Substituted diphenyl butadiynes: a computational study of geometries and electronic transitions using DFT/TD-DFT.

This work is aimed at theoretical understanding of electronic absorption and emission energies of a series of substituted diphenyl butadiynes through an assessment of several TDDFT functionals and a detailed study of solvent effects on their ground and excited state structures and properties. Out of a series of functionals examined, the coulomb attenuated DFT functional CAM-B3LYP is found to be most successful in predicting charge transfer absorption and emission energies of such derivatives. However, TDDFT potential energy surfaces obtained from hybrid functionals such as B3LYP and PBE0 are found to give a good description of the stability of locally excited (LE) and intramolecular charge transfer (ICT) states as a function of torsional angle, for the butadiynyl fluorophores. Interesting structural variations are observed in the ground and excited state optimized geometries of the fluorophores. The ICT emission of the butadiynyl fluorophores is observed to originate from the twisted state where the two phenyl rings in the diphenyl butadiyne get twisted around the butadiyne moiety. A bending of the butadiyne moiety is noted for some of the butadiynyl derivatives in the ICT emissive state. In addition, the direction of absorption and emission transition dipole moment vectors of the butadiynyl fluorophores is found to depend on the nature of substituents present at the periphery of the diphenyl butadiyne moiety.

Pyran-Squaraine as Photosensitizers for Dye-Sensitized Solar Cells: DFT/TDDFT Study of the Electronic Structures and Absorption Properties

In an effort to provide, assess, and evaluate a theoretical approach which enables designing efficient donor-acceptor dye systems, the electronic structure and optical properties of pyran-squaraine as donor-acceptor dyes used in dye-sensitized solar cells were investigated. Ground state properties have been computed at the B3LYP/6-31+G**level of theory. The long-range corrected density functionals CAM-B3LYP, PBEPBE, PBE1PBE (PBE0), and TPSSH with 6-311++G**were employed to examine absorption properties of the studied dyes. In an extensive comparison between experimental results and ab initio benchmark calculations, the TPSSH functional with 6-311++G**basis set was found to be the most appropriate in describing the electronic properties for the studied pyran and squaraine dyes. Natural transition orbitals (NTO), frontier molecular orbitals (FMO), LUMO, HOMO, and energy gaps, of these dyes, have been analyzed to show their effect on the process of electron injection and dye regeneration. Interaction between HOMO and LUMO of pyran and squaraine dyes was investigated to understand the recombination process and charge-transfer process involving these dyes. Additionally, we performed natural bond orbital (NBO) analysis to investigate the role of charge delocalization and hyperconjugative interactions in the stability of the molecule.