Coulomb-attenuating Method Research Articles

Bond dissociation energy of FeCr+ determined through threshold photodissociation in a cryogenic ion trap.

The bond dissociation energy of FeCr+ is measured using resonance enhanced photodissociation spectroscopy in a cryogenic ion trap. The onset for FeCr+ → Fe + Cr+ photodissociation occurs well above the lowest Cr+(6S, 3d5) + Fe(5D, 3d64s2) dissociation limit. In contrast, the higher energy FeCr+ → Fe+ + Cr photodissociation process exhibits an abrupt onset at the energy of the Cr(7S, 3d54s1) + Fe+(6D, 3d64s1) limit, enabling accurate dissociation energies to be extracted: D(Fe-Cr+) = 1.655 ± 0.006eV and D(Fe+-Cr) = 2.791 ± 0.006eV. The measured D(Fe-Cr+) bond energy is 10%-20% larger than predictions from accompanying CAM (Coulomb Attenuated Method)-B3LYP and NEVPT2 and coupled cluster singles, doubles, and perturbative triples electronic structure calculations, which give D(Fe-Cr+) = 1.48, 1.40, and 1.35eV, respectively. The study emphasizes that an abrupt increase in the photodissociation yield at threshold requires that the molecule possesses a dense manifold of optically accessible, coupled electronic states adjacent to the dissociation asymptote. This condition is not met for the lowest Cr+(6S, 3d5) + Fe(5D, 3d64s2) dissociation limit of FeCr+ but is satisfied for the higher energy Cr(7S, 3d54s1) + Fe+(6D, 3d64s1) dissociation limit.

Deeper insights into the density functional theory of structural, optical, and photoelectrical properties using 5-[(4-oxo-4H-chromen-3-yl) methylidene]-4-oxo (thioxo)-6-thioxo-2-sulfido-1, 3, 2-diazaphosphinanes

The structure–activity relationship studied by DFT calculations and contacted with practical antimicrobial results for compounds 1–4 is discussed in detail. In light of this compounds 1–4 have been studied by using DFT/B3LYB/6-311++G (d,p) at the level of theory, the geometrical parameters, bond lengths and bond angles have been discussed. The results of quantum mechanical calculations showed that the presence of phosphorus and sulfur atoms changed the planarity of the parent compound 1 by the range from − 11 to 125°. The electronic parameter and dipole moment of these compounds in the ground state theoretically is analyzed by computing HOMO and LUMO pictures. Using frontier molecular orbital analysis, various spectroscopic and quantum chemical parameters are evaluated. Besides, absorption energies, oscillator strength, and electronic transitions of 1,3,2-diazaphosphinines 1–4 molecules have been derived at TD-DFT/CAM-B3LYP/6-311++G (d,p) computations utilizing, then the CAM-B3LYP method is “the Coulomb-attenuating method bases” set studied the electronic absorption spectra theoretically in the gas phase (TD-DFT) with the polarized split-valence 6-311++G (d, p) basis sets, in addition, the corrected linear response polarizable continuum model and measured experimentally in methanol and cyclohexane indicate a good agreement with the observed spectra (practically) in UV–Vis spectra. The molecular electrostatic potential surfaces plots have been computed to understand reactivity points.

Computational Study on D-π-A-Based Metal-Free Donor-Tuned Molecules for Efficient Organic Dye-Sensitized Solar Cells

In this paper, newly metal-free four donor-[Formula: see text]-acceptor (D-[Formula: see text]-A) molecules (C1D1–C1D4) were designed and used for dye-sensitized solar cells (DSSCs) application, based on literature C1-1. Tetrahydroquinoline, thiophene, and 2-cyanoacrylic acid act as the electron-D, spacer, and electron-A/anchoring groups for all dyes, respectively, while the donor part was tuned and the effect was examined. The density functional theory (DFT) and time-dependent DFT (TD-DFT) have been used on the electronic transitions, geometric structures, absorption properties, electron injection ([Formula: see text]), dye regeneration ([Formula: see text]), light harvesting efficiency (LHE), ground and excited states of dipole moments ([Formula: see text]), open-circuit photovoltage ([Formula: see text]), molecular electrostatic potential (MEP) and Mulliken population analysis (MPA) of the dyes. The TD-DFT method using different functionals with exchange-correlational (XC) and long-range correlated (LC) was calculated to obtain literature data. The computational outcomes have displayed that the Coulomb-attenuating method (CAM-B3LYP) in conjunction with a 6-31G(d,p) basis set was proficient in calculating the UV-Vis spectra of the molecules. The frontier molecular orbitals’ (FMOs) contribution of the HOMOs and LUMOs of C1D1-C1D4 molecules can be confirming positive consequences on the regeneration and electron injection processes. In particular, C1D4 (N(CH3)2) molecule shows a smaller energy gap ([Formula: see text]), longer wavelength, high [Formula: see text] and [Formula: see text]. To conclude, these outcomes display that the calculated C1D1–C1D4 molecules are capable applicants to deliver better performance of the DSSCs.

The ionized states of 6,6-dimethylfulvene; the vibrational energy levels studied by photoionization, configuration interaction and density functional calculations

A new synchrotron-based photoionization spectrum of 6,6-dimethylfulvene shows significant vibrational fine structure (VFS), in contrast to previous studies; this was successfully analysed by Franck-Condon (FC) methods. The sequence of ionic states in the range 7 to 19 eV has been determined by both symmetry adapted cluster configuration interaction and density functional methods, especially using the long-range corrected version of the Becke three-parameter hybrid functional (B3LYP) using the Coulomb-attenuating method (CAM-B3LYP). Both lead to reliable theoretical values for both the calculated vertical and adiabatic ionization energies. The FC profile for the lowest ionization energy (IE1, X2A2) shows extensive VFS which is analysed successfully. The second IE (A2B1) shows truncated structure owing to overlap with IE1.

Investigating the biological actions of some Schiff bases using density functional theory study

Abstract Schiff base ligands have wide varieties of application in several fields. One of which is the biological actions they possess such as anti-fungal, anti-bacterial, anti-malarial, and anti-viral characteristics. In this study, some synthesized phenylimino-based Schiff bases were investigated using density functional theory (DFT) to unravel their biological descriptors. The gas-phase quantum chemical calculation was done on the Schiff base 3-((E)-(phenylimino)methyl)benzene-1,2-diol and other synthesized analogues to evaluate their reactivity and stability properties including the substituent effect on the basic molecule. The Coulomb-attenuating method (CAM-B3LYP) functional was employed for the theoretical calculations. The Nuclear Magnetic Resonance (NMR), Fourier Transform-Infrared (FT-IR), Ultraviolet/visible spectroscopies calculated agrees with the experimental values. The obtained charge transfer and electronic features provide useful information regarding the active sites for biological application in the compounds.

Effects of Substituent and Temperature on the Electronic Properties and Thermodynamics Parameters of 1-(Benzothiazolylamino) Methyl-2-Naphthol: A Computational Study

The effects of substituent and temperature on the 1- (benzothiazolylamino) methyl - 2- naphthol molecules were studied at CAM-B3LYP/6-311G (d,p) level of theory. Selected substitutions were NH2, OH, Me, F, Cl, CHO, COOH, CN and NO2. Substituent effect on the frontier orbitals energies, HOMO-LUMO gap, chemical potential, and electrophilicity were explored. Dependencies of energy changes, reactivity properties and thermodynamics parameters (G, H and S) on the Hammett's constants (p) were provided. Thermodynamics parameters values of the formation reaction were studied reaction at 100-1000 K range. Computational investigation of the substituents and temperature influences on the formation reaction of the 1-(benzothiazolylamino) methyl-2-naphthol showed the negative E values in the studied reactions. Calculated dipole moment values reveal the presence of the EWGs induced a larger dipole moment compared with the EDGs. Higher negative values were found in the presence of EWGs compared to EDGs. Frontier orbitals were stabilized in the presence of EWGs. However, frontier orbitals were destabilized in the presence of EDGs. Thermodynamic analysis revealed that these reactions were non-spontaneous and exothermic. The G and negative H values were increased with increasing the temperature. Optimization and vibrational analysis were done with Gaussian 09 software package. The standard 6-311G(d,p) basis set was considered for the elements, respectively. CAM-B3LYP functional was used for the optimization of the geometries of the compound . This functional is Handy and coworkers’ long range corrected version of B3LYP using the Coulomb-attenuating method The identities of the optimized structures as an energy minimum were confirmed by vibrational analysis

DFT Analysis and Molecular Docking Studies of the Cocrystals of Sulfathiazole-Theophylline and Sulfathiazole-Sulfanilamide

Cocrystals are of immense applications in crystal engineering and pharmaceutical chemistry. Sulfathiazole is found to form cocrystals with theophylline (S1) and sulfanilamide (S2). The experimental and computed values assigned by potential energy distribution. Further natural bond orbital analysis, nonlinear optical properties, frontier molecular orbitals and molecular geometries were also calculated. Frontier orbital energies are used to predict the energy properties and model the possible charge transfer between the cocrystal constituents. The molecular electrostatic potential (MEP) surface reveals the various reactive surfaces in the cocrystal system, which is very important in deciding various biological activities. The ultraviolet-visible (UV-Vis) spectra show the possible electronic transitions of the molecules. Simulated electronic spectra using time dependent density functional theory (TDDFT) method with Coulomb-attenuating method, Becke 3-parameter, Lee-Yang-Parr (CAM-B3LYP) functional was used to investigate the suitability of the cocrystals to be used in dye-sensitized solar cell (DSSC). Moreover docking proves that S1 and S2 cocrystals act as potential inhibitors and paves the way for developing effective drugs.

Band Gap of 3D Metal Oxides and Quasi-2D Materials from Hybrid Density Functional Theory: Are Dielectric-Dependent Functionals Superior?

Reproduction of the band gaps of semiconductors and insulators represents a well-known problem for standard DFT approaches based on semilocal functionals. The problem can be partly solved using hybrid functionals, in which a given portion of exact exchange is mixed with the DFT exchange. Recently, a new class of dielectric-dependent functionals has been introduced in which the amount of exact exchange is derived from the static dielectric function of a given compound. In this study we considered in a systematic way on an equal footing a set of 24 nonmagnetic three-dimensional (3D) bulk metal oxides and 24 quasi-two-dimensional (quasi-2D) semiconductors (oxides, hydroxides, chlorides, oxyhalides, nitrides, and transition metal dichalcogenides) and computed the corresponding Kohn-Sham band gaps with three global hybrid functionals and four range-separated hybrid functionals. These in turn were divided into standard (PBE0, B3LYP, HSE06, SC-BLYP) and dielectric-dependent (DD-B3LYP, DD-SC-BLYP, DD-CAM-B3LYP) functionals. We also performed a statistical analysis of the DFT data set along with structural parameters of these 2D and 3D materials. The surprising result is that overall there is no real improvement with the use of dielectric-dependent functionals compared to PBE0, HSE06, and B3LYP. Short-range DD-SC-BLYP gives a minor improvement in the band gaps for bulk metal oxides compared with standard SC-BLYP, but the mean absolute error is still 0.12 eV higher than with B3LYP. The use of dielectric-dependent standard or short-range functionals such as DD-B3LYP or DD-HSE06 worsens the situation. However, the dielectric-dependent version of the long-range-separated functional implemented with the Coulomb attenuating method (CAM), DD-CAM-B3LYP, leads to a clear improvement for band gaps of quasi-2D materials. On the basis of this analysis, the conclusion is that the use of a standard hybrid functional such as B3LYP or HSE06 is recommended for nonmagnetic bulk 3D metal oxides. On the other hand, the treatment of layered materials such as MoO3 or V2O5 benefits from the use of dielectric-dependent range-separated functionals.

Assessing model-dielectric-dependent hybrid functionals on the antiferromagnetic transition-metal monoxides MnO, FeO, CoO, and NiO

Recently, two nonempirical hybrid functionals, dielectric-dependent range-separated hybrid functional based on the Coulomb-attenuating method (DD-RSH-CAM) and doubly screened hybrid functional (DSH), have been suggested by Chen et al (2018 Phys. Rev. Mater. 2 073803) and Cui et al (2018 J. Phys. Chem. Lett. 9 2338), respectively. These two hybrid functionals are both based on a common model dielectric function approach, but differ in the way how to non-empirically obtain the range-separation parameter. By retaining the full short-range Fock exchange and a fraction of the long-range Fock exchange that equals the inverse of the dielectric constant, both DD-RSH-CAM and DSH turn out to perform very well in predicting the band gaps for a large variety of semiconductors and insulators. Here, we assess how these two hybrid functionals perform on challenging antiferromagnetic transition-metal monoxides MnO, FeO, CoO, and NiO by comparing them to other conventional hybrid functionals and the GW method. We find that single-shot DD0-RSH-CAM and DSH0 improve the band gaps towards experiments as compared to conventional hybrid functionals. The magnetic moments are slightly increased, but the predicted dielectric constants are decreased. The valence band density of states (DOS) predicted by DD0-RSH-CAM and DSH0 are as satisfactory as HSE03 in comparison to experimental spectra, however, the conduction band DOS are shifted to higher energies by about 2 eV compared to HSE03. Self-consistent DD-RSH-CAM and DSH deteriorate the results with a significant overestimation of band gaps.

Quantum chemical calculations, Hirshfeld surface analysis, and molecular docking studies of antibacterial (E)-N′-((1H-Indol-3-yl)methylene)-4-bromobenzohydrazide

The theoretical parameters such as optimized geometrical parameters (bond lengths, bond angles, and dihedral angles), vibrational assignments, non-linear optical property, natural population analysis, and global chemical descriptors were calculated using the density functional theory with Becke, 3-parameter, Lee-Yang-Parr functional and Coulomb-attenuating method. Spectroscopic characterization of (E)-N′-((1H-Indol-3-yl)methylene)-4-bromobenzohydrazide was investigated by the Fourier transform infrared analysis with the potential energy distribution, proton nuclear magnetic resonance, and ultraviolet-visible techniques. The intermolecular interactions of the title molecule in the crystal structure were visualized by the three-dimensional Hirshfeld surface and associated two-dimensional fingerprint plots. In order to understand molecular stability, global reactive properties calculated at the time-dependent density functional theory have been investigated by visualization of frontier molecular orbitals. In addition, the first-order hyperpolarizability has been investigated to understand the non-linear optical activity of the molecule. Molecular docking studies supporting the antibacterial activity of the title molecule give a high-binding energy value of −5.20 kcal/mol due to the interaction of the carbonyl group with the target protein.

Accurate equilibrium structures of methyl methacrylate and methacrylic acid by microwave spectroscopy and dispersion corrected calculations.

The rotational constants of s-trans and s-cis methyl methacrylate and methacrylic acid are determined from microwave spectra. All singly substituted heavy-atom isotopologs of the four species are measured in natural abundance. The experimental rotational constants are combined with anharmonic vibrational corrections using the Coulomb-attenuating method, Becke, three-parameter, Lee-Yang-Parr density functional with Grimme's D3 dispersion corrections and the Becke-Johnson damping function, yielding precise semi-experimental equilibrium rotational constants. These constants are used to determine semi-experimental equilibrium structures with sub-picometer accuracy, suitable for benchmarking purposes.

TD-DFT Calculations, NBO, NLO Analysis and Electronic Absorption Spectra of Some Novel Thiazolo[3,2-a]Pyridine Derivatives Bearing Anthracenyl Moiety

The electronic structure and spectra of the studied compounds 1–4 are investigated using TD-DFT/B3LYB/6-311G (d, p) level of theory. The results of calculations show that all the studied compounds 1–4 are non-planar, as indicated from the dihedral angles. The electronic absorption spectra of the studied compounds are recorded in the UV-VIS region, in both Acetone (as polar solvent) and Xylene (as non-polar solvent). The observed vertical electronic transitions assignments are facilitated via time-dependent density functional theory TD-DFT. Solvent dependence of the band maxima (λmax) and intensities of the observed spectra are explained in terms of blue and red shifts. Electronic configurations contributing to each excited state are identified and the relevant MOs are characterized. The natural bond orbital (NBO) analysis were discussed in terms of the extent of delocalization, intermolecular charge transfer and second order perturbation interactions between donor and acceptor MOs. The Coulomb-attenuating method (CAM-B3LYP) and Corrected Linear Response Polarizable Continuum Model (CLR) PCM studied for theoretically obtaining the electronic absorption spectra in gas phase, Acetone and Xylene, respectively, indicate a good agreement with the observed spectra. The calculated nonlinear optical parameters (NLO); polarizibilty (α), anisotropy of the polarizibility (Δα) and first order hyperpolarizibility (β) of the studied compounds show promising optical properties. The HOMO-LUMO energy gap helped in analyzing the chemical reactivity, hardness, softness, chemical potential and electro negativity. 3D-plots of the molecular electrostatic potential (MEP) for the studied compounds are investigated and analyzed showing the distribution of electronic density of orbital's describing the electrophilic and nucleophilic sites of the selected molecules.

TD-DFT calculations, electronic structure, natural bond orbital analysis, nonlinear optical properties electronic absorption spectra and antimicrobial activity application of new bis-spiropipridinon/pyrazole derivatives

A new bis-spiropipridinon/pyrazole compound and some of its derivatives are characterized in terms of several theoretical parameters such as density of states (DOS), molecular electrostatic potentials (MEPs), non-linear optical (NLO) properties and electrophilicity. The electronic structure and nonlinear optical properties of the studied compounds 1-5 are investigated theoretically at the DFT-B3LYP/6-311G(d,p) level of theory. The effect of substituents of different strengths on the geometry and energetic are analyzed and discussed. The static dipole moment (µ), polarizability (α), anisotropy polarizability (Δα), and first order hyperpolarizability (βtot), are parameters for NLO of the studied compounds have been calculated at the same level of theory and compared with the prototype para-nitro-aniline (PNA). The electronic absorption spectra of the studied compounds are recorded in the UV-VIS region, in both ethanol and dioxane solvents. The theoretical spectra computed at a new hybrid exchange-correlation functional using the Coulomb-attenuating method (CAM-B3LYP) at the 6-311G(d,p) bases set in gas phase and with the polarizable continuum model (PCM) in dioxane and ethanol indicate a good agreement with the observed spectra. The antimicrobial activity for studied compounds was investigated. The antimicrobial activity results revealed that compound 4 has a good potency against Gram positive bacteria (E. coli) and Gram negative bacteria (P. vulgaris) in comparison with doxymycin standard. The structure activity relationship SAR has been studied for the studied compounds by DFT calculations, moreover, confirmed practical antimicrobial activity results.

Computational Characterization of "Dark" Intermediates in the Ultrafast Deactivation of Photoexcited Bilirubin.

The characterization of various intermediates in the ultrafast deactivation of photoexcited ( Z, Z)-bilirubin-IXα was carried out using different computational methods. Various excited states of ( Z, Z)-bilirubin-IXα and their respective vertical excitation energies were calculated using time-dependent density functional theory (TD-DFT) employing the Coulomb-attenuating method (CAM) combined with the B3LYP functional, which is known to predict accurate results on the charge transfer excitation process. Optimized geometries and absorption spectra were determined in chloroform solvent using the polarizable continuum model incorporating the integral equation formalism. The optimized geometries of different conformers of bilirubin ( ZZ, ZE, EZ, and EE) along with their relative energies and vertical excitation energies were obtained. The geometry of the first excited state, S1, for the ZZ conformer was optimized using TD-DFT. The computational study suggests that excited-state intramolecular proton transfer (ESIPT) plays a major role in the deactivation process of ( Z, Z)-bilirubin-IXα on a shorter time scale. The lactam-lactim tautomerism that arises from the ESIPT process gives rise to various intermediates of ( Z, Z)-bilirubin-IXα. The computational results nicely corroborate the experimental findings available in the literature.

Insights into Excited State Intramolecular Proton Transfer: An Alternative Model for Excited State Proton Transfer of Green Fluorescence Protein

The excited state intramolecular proton transfer (ESIPT) that occurs in the o-sulfonamide analogue ( o-TsABDI) of the green fluorescent protein (GFP) chromophore provides an alternative model to get insights into the excited state proton transfer (ESPT) related photophysics of GFP. In this article, we explored the ESIPT-related photophysics of o-TsABDI by electronic absorption and fluorescence emission spectra in a wide polarity range of solvents, cis- trans photoisomerization experiment, and Coulomb-attenuating method (CAM)/time-dependent (TD) density functional theory (DFT) calculations. We found that the whole ESIPT process involves four steps. The first step is photoexcitation of o-TsABDI, which does not involve charge transfer (CT). The second step is ESIPT and accompanying electron transfer from the n orbital of the sulfonamide nitrogen to the half-filled π orbital of the 4-benzylideneimidazolone moiety. The third step is fluorescence emission of the zwitterionic o-TsABDI and accompanying CT from the π* orbital of the 4-benzylideneimidazolone moiety to the half-filled n orbital of the sulfonamide nitrogen. The last step involves irreversible and barrierless proton recombination. In contrast to the isolated GFP chromophore and its p- and m-amino analogues, the S1 excited state of o-TsABDI does not relax by way of cis- trans photoisomerization through the S1/S0 conical intersection CI(I) by rotating around the I-bond, but follows the ESIPT pathway. The low fluorescence quantum yield of the zwitterionic o-TsABDI might be due to (1) the fluorescence that involves the low-probability π* → n charge transfer and (2) nonradiative relaxation through the S1/S0 conical intersection CI(P″) by rotating around the P-bond.

A general range-separated double-hybrid density-functional theory.

A range-separated double-hybrid (RSDH) scheme which generalizes the usual range-separated hybrids and double hybrids is developed. This scheme consistently uses a two-parameter Coulomb-attenuating-method (CAM)-like decomposition of the electron-electron interaction for both exchange and correlation in order to combine Hartree-Fock exchange and second-order Møller-Plesset (MP2) correlation with a density functional. The RSDH scheme relies on an exact theory which is presented in some detail. Several semi-local approximations are developed for the short-range exchange-correlation density functional involved in this scheme. After finding optimal values for the two parameters of the CAM-like decomposition, the RSDH scheme is shown to have a relatively small basis dependence and to provide atomization energies, reaction barrier heights, and weak intermolecular interactions globally more accurate or comparable to range-separated MP2 or standard MP2. The RSDH scheme represents a new family of double hybrids with minimal empiricism which could be useful for general chemical applications.

Theoretical Study and Experimental Analysis on 2-(1-Ethyl-4-hydroxy-2-oxo-1,2-dihydroquinolin-3-yl)-2-oxoacetic Acid (3) Using the DFT Approach

Riley oxidation of 3-acetyl-4-hydroxyquinolin-2(1H)-one (1) with selenium dioxide furnished the unexpected product 2-(1-ethyl-4-hydroxy-2-oxo-1,2-dihydroquinolin-3-yl)-2-oxoacetic acid (3). The expected product 2-(1-ethyl-4-hydroxy-2-oxo-1,2-dihydroquinolin-3-yl)-2-oxoacetaldehyde (2) was excluded based on the spectral data. The elemental analysis and spectral data (IR, and 1H NMR) was used to deduce the structure of compound 3. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations of the electronic structure at the B3LYP/6-311G (d,p) level of theory have been employed for compound 3 to investigated its geometry, linear polarizability 〈Δα〉, first-order hyperpolarizability 〈β〉, natural bonding orbital (NBO), molecular electrostatic potential contours (MEP and ESP), electrophilicity, and UV–Vis spectra in both ethanol and dioxane solvents. The geometrical and energetic parameters have been extensively investigated to reveal the reason behind the selective formation of compound 3, rather than the expected product 2. FT-IR spectra in the solid phase were recorded for compound 3. The thermo-chemical parameters, harmonic vibration frequencies, and the equilibrium geometries have been calculated at the DFT/B3LYP/6-311G (d,p) level. Time-dependent density functional theory (TD-DFT) was used to calculate the excited states of compound 3. Changes in the solvent cause changes in the band intensities and in the positions of the band maxima (λmax). The excited state was identified and contributes to the electronic configurations, and it was characterized in terms of the relevant MOs. The theoretical spectra were computed using the Coulomb-attenuating method (CAM-B3LYP), using the basis set 6-311G (d,p) in the gas phase, and the polarizable continuum model (PCM) in dioxane and ethanol. The results indicate good agreement with the observed spectra.

TD-DFT calculations, NBO analysis and electronic absorption spectra of some thiazolo[3,2-a]pyridine derivatives

The electronic structure of thiazolo[3,2-a]pyridine and some of its derivatives are investigated theoretically using B3LYB/6-311G (d, p) method. The calculations show that all the studied compounds 1–5 are non-planar, as indicated from the dihedral angles. The electronic absorption spectra of the studied compounds are recorded in the UV–VIS region, in both DMF and Dioxane solvents. Assignments of the observed electronic transitions are facilitated via time-dependent density functional theory (TD-DFT) computations. Band maxima (λmax) and intensities of the spectra are found to have solvent dependence reflected as blue and red shifts. Electronic configurations contributing to each excited state are identified and the relevant MOs are characterized. The extent of delocalization and intermolecular charge transfer are estimated and discussed in terms of natural bond orbital (NBO) analysis and second order perturbation interactions between donor and acceptor MOs. The theoretical spectra computed at “A new hybrid exchange-correlation functional using the Coulomb-attenuating method (CAM-B3LYP),” at the 6-311G (d, p) bases set in gas phase and with the Polarizable Continuum Model (PCM) in Dioxane and DMF indicate a good agreement with the observed spectra.

DFT and TD-DFT calculation of new thienopyrazine-based small molecules for organic solar cells.

BackgroundNovel six organic donor-π-acceptor molecules (D-π-A) used for Bulk Heterojunction organic solar cells (BHJ), based on thienopyrazine were studied by density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches, to shed light on how the π-conjugation order influence the performance of the solar cells. The electron acceptor group was 2-cyanoacrylic for all compounds, whereas the electron donor unit was varied and the influence was investigated.MethodsThe TD-DFT method, combined with a hybrid exchange-correlation functional using the Coulomb-attenuating method (CAM-B3LYP) in conjunction with a polarizable continuum model of salvation (PCM) together with a 6-31G(d,p) basis set, was used to predict the excitation energies, the absorption and the emission spectra of all molecules.ResultsThe trend of the calculated HOMO–LUMO gaps nicely compares with the spectral data. In addition, the estimated values of the open-circuit photovoltage (Voc) for these compounds were presented in two cases/PC60BM and/PC71BM.ConclusionThe study of structural, electronics and optical properties for these compounds could help to design more efficient functional photovoltaic organic materials.

Towards quantifying the role of exact exchange in the prediction hydrogen bond spin-spin coupling constants involving fluorine.

The effect of a fraction of Hartree-Fock exchange on the calculated spin-spin coupling constants involving fluorine through a hydrogen bond is analyzed in detail. Coupling constants calculated using wavefunction methods are revisited in order to get high-level calculations using the same basis set. Accurate MCSCF results are obtained using an additive approach. These constants and their contributions are used as a reference for density functional calculations. Within the density functional theory, the Hartree-Fock exchange functional is split in short- and long-range using a modified version of the Coulomb-attenuating method with the SLYP functional as well as with the original B3LYP. Results support the difficulties for calculating hydrogen bond coupling constants using density functional methods when fluorine nuclei are involved. Coupling constants are very sensitive to the Hartree-Fock exchange and it seems that, contrary to other properties, it is important to include this exchange for short-range interactions. Best functionals are tested in two different groups of complexes: those related with anionic clusters of type [F(HF)n](-) and those formed by difluoroacetylene and either one or two hydrogen fluoride molecules.