Search

A new descriptor tool enabling to qualitatively identify excited-state potential energy regions with high decay probability is here disclosed and applied to analyze a photoinduced ring-opening reaction already well characterized from the experimental and theoretical point of view. The analysis based on such descriptor allows one to highlight a high probability of excited-state deactivation within the Franck–Condon region, in agreement with experiments, and to qualitatively indentify the main mechanisms providing efficient pathways of photoreactivity. [ABSTRACT FROM AUTHOR]

The interaction of the lithium alkaline metal, with the benzene molecule, is herein investigated in the framework of density functional theory (DFT) method. Performances of a large set of exchange–correlation functionals in reproducing some physical properties are benchmarked using as reference the CCSD(T) method at the complete basis set limit (CCSD(T)/CBS). Both the cationic and neutral lithium–benzene systems (LiBz+ and LiBz) are considered as well as the sandwich compound (BzLiBz+). Among all the functionals, ωB97X emerges as the best approach for modeling all the three systems analyzed, while large deviations are observed for several functionals in the case of the problematic neutral Li–benzene system. Particular attention was devoted to the discussion of the results obtained with methods containing empirical dispersion corrections. More broadly, our results underline the difficulties and the limits of current DFT approaches in the description of the interaction of Li with aromatic molecules, which is relevant in several applied fields. [ABSTRACT FROM AUTHOR]

Periodic density functional theory (DFT) and hybrid ONIOM time-dependent DFT/MM cluster calculations have been carried out to investigate the ground- and excited-state properties of the crystalline structures of the enolic and ketonic tautomeric forms of a propoxy-substituted dibenzothiazolylphenol molecule (OPr), a prototype for systems undergoing the excited-state intramolecular proton transfer process. The crystalline structures of the tautomeric forms are well reproduced and, as expected, at the ground state, the enol polymorph is predicted to be more stable than the keto one. At the excited state, the effect of the environment on time-dependent DFT calculations has been accounted for by including a charge embedding scheme, and the influence of different kinds of point charges (Mulliken, CM5, RESP and QEq) in determining the optical properties of the central molecule has been investigated. The results reveal that, in fair agreement with experimental data, the absorption (emission) energies of the enol (keto) OPr molecule is red-shifted of about 3 (3) nm going from the gas phase to chloroform and blue-shifted of 10 (23) nm going from the gas to the crystal phase when the electronic embedding with Mulliken charges is employed. The electrostatic embedding influences the excited-state properties more severely than the ground-state properties, and apart the QEq charges, all other models provide Stokes shifts in reasonable agreement with experimental data. [ABSTRACT FROM AUTHOR]

This contribution focuses on bulk band gap and dielectric response calculations for copper phosphide Cu3P, using hybrid functionals and linear response DFT+U methods, considering both plane wave and Gaussian-type orbitals basis sets. The semiconducting state of Cu3P is reproduced in good quantitative agreement with experiments when using these methods, at variance with the description provided by standard DFT calculations based on GGA functionals, predicting Cu3P to be a semimetal. Additional DFT+U calculations were performed on zinc blende cadmium selenide CdSe, to further investigate the effect of U on semiconducting binary compounds. For both Cu3P and CdSe, the materials' band gap depends strongly on the on-site repulsion of the nonmetal unfilled p-orbitals, while hybrid functionals still perform well. This suggests that the use of the Hubbard term in DFT+U calculations should be carefully checked for all elements when dealing with semiconducting binary compounds. [ABSTRACT FROM AUTHOR]

In view of their promising photosensitizing features, expanded porphyrins are gaining wide attention for their potential use both in photodynamic therapy of cancer and as likely photoactivated agent for water disinfection. Herein, we report a joint experimental and theoretical investigation on the 20-(4′-carboxyphenyl)-2,13-dimethyl-3,12-diethyl-[22] pentaphyrin complex 4. The synthesis, NMR, UV–Vis and mass characterization of the new compound together with a detailed theoretical investigation of the photophysical properties, are presented. In particular, type I and type II photoreactions have been explored by means of DFT and its TDDFT formulation characterizing the electronic absorption spectra, providing singlet–triplet energy gap, vertical ionization potential and electron affinity. Results show that title compound is able to generate the cytotoxic singlet oxygen species supporting the application of the proposed molecule as a photoactivated agent for water disinfection. [ABSTRACT FROM AUTHOR]

In this work, we present application of a previously proposed DFT-based computational protocol to a series of four push–pull type organic dyes for DSSC application, among which two are newly introduced here. Dyes investigated all use cyanoacrylic acid and dithiafulvene as the acceptor and donor subunits, respectively, and differ by their π-spacer: phenyl (DTF-C1), phenyl-thiophene-phenyl (DTF-C3), phenyl-furan-phenyl (DTF-C5), phenyl-N-ethyl pyrrole-phenyl (DTF-C6), making an investigation of the role of the π-bridge characteristics, including length and electronic structures, on the performances of DSSC systems possible. Investigated properties included UV–visible spectra of isolated dyes, and important macroscopic DSSC experimental data such as injection times, incident photon-to-current conversion efficiencies and short-circuit photocurrents derived from the adsorption of these dyes on a water-passivated TiO2 surface. Fairly good agreements between the computational and experimental results have been obtained. Furthermore, from the computed data, we predict that one of the newly introduced dyes is an excellent candidate for DSSC application, with expected photoconversion efficiencies higher than those previously achieved for this sensitizer series. [ABSTRACT FROM AUTHOR]

The performances of two parametrized functionals (namely B3LYP and B2PYLP) have been compared with those of two non-parametrized functionals (PBE0 and PBE0-DH) on a relatively large benchmark set when three different types of dispersion corrections are applied [namely the D2, D3 and D3(BJ) models]. Globally, the MAD computed using non-parametrized functionals decreases when adding dispersion terms although the accuracy not necessarily increases with the complexity of the model of dispersion correction used. In particular, the D2 correction is found to improve the performances of both PBE0 and PBE0-DH, while no systematic improvement is observed going from D2 to D3 or D3(BJ) corrections. Indeed when including dispersion, the number of sets for which PBE0-DH is the best performing functional decreases at the benefit of B2PLYP. Overall, our results clearly show that inclusion of dispersion corrections is more beneficial to parametrized double-hybrid functionals than to non-parametrized ones. The same conclusions globally hold for the corresponding global hybrids, showing that the marriage between non-parametrized functionals and empirical corrections may be a difficult deal. [ABSTRACT FROM AUTHOR]

The performances of a family of recently developed generalized gradient approximation (GGA) functionals based on the Tognetti–Cortona–Adamo (TCA) family and making use of the gradient-regulated connection (GRAC) approach are here tested on an uncommon benchmark set for the prediction of transition state (TS) structures and energies of a series of four reactions involving an early transition metal (Zr, d0). This benchmark test thus represents the first step in the organometallic world in which dn ions allowing complex phenomena such as spin crossover represent the higher level of complexity. The results obtained show that the performances of the GRAC-xxx functionals are comparable to those of global hybrid functionals both in the prediction of reaction barriers and of structural features of TSs. More complex functional forms (such as range-separated hybrids) in average enhance the energetic features, but not necessarily the overall accuracy on calculated structures. On the other hand, and as expected, purposely developed functionals for the prediction of chemical reactivity provide both structural and energetic features in good agreement with post-HF results. The present study, besides proving the good performances of GGA functionals of the GRAC-TCA family for the prediction of TS structural parameters and energetics of metal containing systems, also underlines the importance of the use of diversified benchmark sets to allow a fair evaluation of functionals performances. [ABSTRACT FROM AUTHOR]

The performances of two range-separated functionals (HISS-A and HISS-B), recently developed by Savin and collaborators, and including a fraction of HF exchange for an intermediate range of interelectronic distance, have been tested for the prediction of vertical excited state energies over three benchmark sets of molecules mainly probing valence and intramolecular charge-transfer transitions in small- to medium-size organic compounds. The results obtained show that HISS-B outperforms HISS-A providing results that are, for singlet-to-singlet excitations, at least in line with those of more traditional long-range-separated hybrids such as LC-PBE or CAM-B3LYP possessing the correct asymptotic behavior and, in the case of larger compounds, close to those provided by global hybrids. [ABSTRACT FROM AUTHOR]

A new type of generalized gradient approximation exchange functional coupled with the TCA correlation model has been proposed. Based on gradient-regulated connection, this exchange functional is able to mix performances of a modified PBE for the bulk region, to those of the PW91 for the asymptotic one, leading to a significant improvement on the modelization of weak interacting systems, while keeping a good accuracy for the atomization energies. [ABSTRACT FROM AUTHOR]

The interaction of H molecules with a Cu(100) metallic surface has been investigated by DFT approaches using a (H)Cu cluster model. Nine exchange-correlation functionals, belonging to the generalized gradient approximations (GGA), meta GGA (mGGA), hybrid Kohn-Sham/Hartree-Fock models, either based on GGAs or mGGAs, range-separated hybrids, and double-hybrid families, have been tested on the chemisorption and physisorption processes involving one or two H layers. The addition of an empirical correction for dispersion has also been tested for some of these functionals. The calculated energies and structural parameters were compared to sophisticated multi reference configuration interaction including Davidson's correction for quadruple excitations (MRCI + Q). Our results show that among the nine considered exchange-correlation functionals, none can accurately reproduce all processes involved in the successive layers adsorption. Although an hybrid based on a mGGA such as M06-2X can quantitatively describe both the physisorption step and dissociation barriers involved in the adsorption of the first H, it fails to reproduce its chemisorption. On the other hand, significant discrepancies with the reference post-HF data are obtained for the description of the second layer interaction, no matter which functional is considered, outlining the need of improvement and/or development of exchange-correlation functionals suitable for complex systems such as H/HCu. [ABSTRACT FROM AUTHOR]

With the aim of designing new inorganic photosensitizers for photovoltaic applications, the structural and electronic properties of two Ru(II) complexes containing terpyridine-based ligands derived from expanded pyridiniums both branched-polyphenyl-and fused-polycyclic-were investigated by the means of density functional theory (DFT) and time-dependent DFT (TD-DFT). In particular, the structure and electronic absorption of the fused architectures-including the isolated ligand and its complex-were compared with those of their respective branched precursors with the aim to account for the their enhanced electronic features in the visible spectral region. The theoretical insights gained into the 'large-surface' ligand and its associated complex open the route for a joint experimental and theoretical design of new inorganic photosensitizers based on fused expanded pyridiniums. [ABSTRACT FROM AUTHOR]

We benchmark three recently proposed range-separated hybrids, namely ωB97, ωB97X and ωB97XD in the framework of time-dependent density functional theory simulations of electronic absorption spectra. Comparisons are made with both theoretical estimates obtained by highly correlated approaches and experimental wavelengths of maximal absorption measured for important classes of $$\pi \rightarrow \pi^\ast$$ and $$n \rightarrow \pi^\ast$$ chromogens. The amplitude of the errors induced by the lack of vibronic coupling in our computational model is also evaluated for five dyes. The performances of the ωB97 group are systematically compared to the results of other global and range-separated hybrids. It turns out that ωB97XD provides, in general, more accurate estimates than ωB97X and ωB97. [ABSTRACT FROM AUTHOR]

We have assessed the performances of three recently proposed functionals, RC (Ragot and Cortona in J Chem Phys 121:7671, ), TCA (Tognetti et al. in J Chem Phys 128:034101, ), and RevTCA (Tognetti et al. in Chem Phys Lett 460:536, ) by calculating the activation enthalpies for ten pericyclic reactions and eighteen 1,3-dipolar cycloadditions. We have found that the local functional (RC) gives results only marginally better than the local-density approximation ones, while the two GGA functionals, TCA and RevTCA, both strongly improve the results with respect to PBE. The performances of RevTCA, in particular, are not far different from those of a hybrid functional such as B3LYP. [ABSTRACT FROM AUTHOR]

A new neutral gene vector, based on a lipopolythiourea N-(2-(3-[2-(2-(3-[2-(3-methyl-thioueido)-ethyl] -thioureido)-ethylamino)-ethyl]-thioureido)-ethyl)- N′, N′- ditetradecyl-succinamide (DTTU) has recently been synthetized but its behavior is difficult to study at the experimental level. Density functional theory (DFT) calculations have thus been performed to predict its interaction mode with B-DNA. Its acidic properties are first computed and suggest that DTTU should be non-charged when interacting with DNA. Different ways of DTTU/DNA associations based on hydrogen bonding–namely external and groove-binding interactions—are then investigated. Our calculations clearly point out that external interaction is preferred with respect to groove-binding, due to three bifurcated hydrogen bonds between DTTU thiourea groups and DNA phosphates. Such results can be explained by the absence of charged groups in groove-binding whereas the negative charge of DNA phosphates deeply strengthens hydrogen bonds. [ABSTRACT FROM AUTHOR]

Using an ab intio TD-DFT approach systematically accounting for the molecular surroundings effects, we have computed the n → π* absorption wavelength of 22 azoalkane derivatives. For the complete set of molecules, we propose a theoretical procedure able to reproduce the major auxochromic effects, and to deliver a mean absolute error of 5.8 nm (0.056 eV) with maximal deviations limited to 21 nm (0.20 eV). The impact of including in the model explicit solvent molecules is discussed as well. This contribution confirms that PCM-TD-PBE0 is a first-grade method for simulating the vertical absorption spectra of organic dyes. [ABSTRACT FROM AUTHOR]

Water solvation effects on theoretical binding energies of the tetramethylammonium cation with benzene, phenol and indole have been analyzed as a prototype of biological cation–π interactions. Solvent effects were introduced in the quantum chemical computations either by considering molecules belonging to the first solvation of the tetramethylammonium or by a polarizable continuum model. Our results show that the calculated binding energies are reduced by about three quarters with respect to the corresponding gas-phase results, but the sequence benzene

The reactivity of two significant classes of organometallic compounds involved in electrochemical processes, namely Co(II) N4-macrocycles and Ru/Os polypyridyl complexes, toward the oxidation of two different electron donor molecules (2-mercaptoethanol and iodine) was investigated using first-principle theoretical methods. Two different descriptors, the donor-acceptor intermolecular hardness and the electrophilicity index, were considered for discriminating the relative reactivity of the different species toward the same electron donor. All of the calculations were carried out using a recent hybrid Hartree-Fock/Density Functional approach (PBE0) and solvent effects were included using a recent version of the polarisable continuum model (C-PCM). The influences of the metal atom, of the chemical environment, and of the medium on reactivity were analysed and compared to the available experimental data. [ABSTRACT FROM AUTHOR]