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This article compares two double-hybrid density functionals, r2SCAN-QIDH and SOS1-r2SCAN-QIDH-D4, and explains their terminology. The r2SCAN-QIDH model is a nonempirical DH model derived from adiabatic-connection formalism and second-order perturbation theory, while the SOS1-r2SCAN-QIDH-D4 model includes an empirical dispersion term. The article evaluates the performance of these models on different benchmark datasets and finds that the r2SCAN-QIDH model is accurate, while the dispersion-corrected variant is more efficient for noncovalent interactions. The article emphasizes the importance of using accurate terminology to avoid confusion between different DH approaches. The document also discusses the development of NL and D4 dispersion correction parameters for noncovalent interactions, providing tables with data from the GMTKN55 database. [Extracted from the article]

In this Communication, we assess a panel of 18 double-hybrid density functionals for the modeling of the thermochemical and kinetic properties of an extended dataset of 449 organic chemistry reactions belonging to the BH9 database. We show that most of DHs provide a statistically robust performance to model barrier height and reaction energies in reaching the "chemical accuracy." In particular, we show that nonempirical DHs, such as PBE0-DH and PBE-QIDH, or minimally parameterized alternatives, such as ωB2PLYP and B2K-PLYP, succeed to accurately model both properties in a balanced fashion. We demonstrate, however, that parameterized approaches, such as ωB97X-2 or DSD-like DHs, are more biased to only one of both properties. [ABSTRACT FROM AUTHOR]

We recently derived a new and simple route to the determination of the range-separation parameter in range-separated exchange hybrid and double-hybrid density functionals by imposing an additional constraint to the exchange-correlation energy to recover the total energy of the hydrogen atom [Brémond et al., J. Chem. Phys. 15, 201102 (2019)]. Here, we thoroughly assess this choice by statistically comparing the derived values of the range-separation parameters to the ones obtained using the optimal tuning (OT) approach. We show that both approaches closely agree, thus, confirming the reliability of ours. We demonstrate that it provides very close performances in the computation of properties particularly prone to the one- and many-electron self-interaction errors (i.e., ionization potentials). Our approach arises as an alternative to the OT procedure, conserving the accuracy and efficiency of a standard Kohn–Sham approach to density-functional theory computation. [ABSTRACT FROM AUTHOR]

In this communication, we present a new and simple route to derive range-separated exchange (RSX) hybrid and double hybrid density functionals in a nonempirical fashion. In line with our previous developments [Brémond et al., J. Chem. Theory Comput. 14, 4052 (2018)], we show that by imposing an additional physical constraint to the exchange-correlation energy, i.e., by enforcing to reproduce the total energy of the hydrogen atom, we are able to generalize the nonempirical determination of the range-separation parameter to a family of RSX hybrid density functionals. The success of the resulting models is illustrated by an accurate modeling of several molecular systems and properties, like ionization potentials, particularly prone to the one- and many-electron self-interaction errors. [ABSTRACT FROM AUTHOR]

We propose two analytical expressions aiming to rationalize the spin-component-scaled (SCS) and spin-opposite-scaled (SOS) schemes for double-hybrid exchange-correlation density-functionals. Their performances are extensively tested within the framework of the nonempirical quadratic integrand double-hybrid (QIDH) model on energetic properties included into the very large GMTKN30 benchmark database, and on structural properties of semirigid medium-sized organic compounds. The SOS variant is revealed as a less computationally demanding alternative to reach the accuracy of the original QIDH model without losing any theoretical background. [ABSTRACT FROM AUTHOR]

We investigate the performance of a set of recently introduced range‐separated double‐hybrid functionals, namely ωB2‐PLYP, ωB2GP‐PLYP, RSX‐0DH, and RSX‐QIDH models for hard‐to‐calculate excitation energies. We compare with the parent (B2‐PLYP, B2GP‐PLYP, PBE0‐DH, and PBE‐QIDH) and other (DSD‐PBEP86) double‐hybrid models as well as with some of the most widely employed hybrid functionals (B3LYP, PBE0, M06‐2X, and ωB97X). For this purpose, we select a number of medium‐sized intra‐ and inter‐molecular charge‐transfer excitations, which are known to be challenging to calculate using time‐dependent density‐functional theory (TD‐DFT) and for which accurate reference values are available. We assess whether the high accuracy shown by the newest double‐hybrid models is also confirmed for those cases too. We find that asymptotically corrected double‐hybrid models yield a superior performance, especially for the inter‐molecular charge‐transfer excitation energies, as compared to standard double‐hybrid models. Overall, the PBE‐QIDH and its corresponding range‐separated RSX‐QIDH functional are recommended for general‐purpose TD‐DFT applications, depending on whether long‐range effects are expected to play a significant role. [ABSTRACT FROM AUTHOR]

A comprehensive theoretical investigation of the MLaNb2O7 (M = H, Li, Na, K, Rb, and Cs) series of ion-exchangeable layered perovskite is presented. These perovskites are in particular interesting in view of their potential applications as inorganic supports for the design of new hybrid inorganic-organic proton conductors. In particular, their structural and electronic properties have been investigated by periodic calculations in the framework of Density Functional Theory, using different exchange-correlation functionals. A general very good agreement with the available experimental (XRD, NPD, and EXAFS) data has been found. The structure of the protonated HLaNb2O7 form has also been further clarified and a new tetragonal space group is proposed for this compound, better reproducing the experimental cell parameters and yielding to a more realistic picture of the system. The electronic investigation highlighted that all the compounds considered are very similar to each other and that the interaction between interlayer cations and perovskite slabs is purely ionic, except for the proton that is, instead, covalently bound. [ABSTRACT FROM AUTHOR]

DH‐SVPD is a tailored atomic basis set originally developed to enhance the domain of applicability of double‐hybrid density functionals to large molecular systems in weak interactions. In combination with any density functional belonging to this approximation, it provides an accurate estimate of noncovalent interaction energies at the cost of a double‐ζ basis set, without adding a posteriori an empirical dispersion correction. Here, we show that the accuracy/cost ratio observed previously for energy properties can be safely extended to the modeling of structural parameters of small‐ and medium‐sized organic molecules. In particular, we demonstrate that, in combination with the nonempirical PBE‐QIDH double hybrid, DH‐SVPD is competitive with very large quadruple‐ζ basis sets when modeling both covalent and noncovalent structural parameters. [ABSTRACT FROM AUTHOR]

We investigate here the lowest‐energy (spin‐conserving) excitation energies for the set of He‐Ne atoms, with the family of nonempirical PBE, PBE0, PBE0‐1/3, PBE0‐DH, PBE‐CIDH, PBE‐QIDH, and PBE0‐2 functionals, after employing a wide variety of basis sets systematically approaching the basis set limit: def2‐nVP(D), cc‐pVnZ, aug‐cc‐pVnZ, and d‐aug‐cc‐pVnZ. We find that an accuracy (ie, mean unsigned error) of 0.3 to 0.4 eV for time‐dependent density functional theory (DFT) atomic excitation energies can be robustly achieved with modern double‐hybrid methods, which are also stable with respect to the addition of a double set of diffuse functions, contrarily to hybrid versions, in agreement with recent findings employing sophisticated multiconfigurational DFT methods. [ABSTRACT FROM AUTHOR]

A new double hybrid functional is herein presented, in which the ratio of the Hartree-Fock, Kohn-Sham, and perturbation terms (MP2) is determined on the basis of physical considerations. This functional, denominated PBE0 Double Hybrid (PBE0-DH), contains a small MP2 contribution (12.5%) and it has been tested on a number of different molecular properties, including atomization energies, weak interactions, and reaction energies. From the obtained results, PBE0-DH seems to represent a significant improvement with respect to the parent PBE0 functional, a parameter-free hybrid. Overall its performances are comparable to the ones found using other parameterized double hybrids. From a more general point of view, our work points out that, already showed for classes of other functionals, reliable and general-purpose double hybrids can be obtained on purely theoretical bases, without the use of any empirical fitting. [ABSTRACT FROM AUTHOR]

In this work, we present the application of the hybrid short-range density functional theory/long-range MP2 energy gradients to the bond length alternation in polymethineimine and polyacetylene conjugated oligomers. Compared to other density functional calculations, our results are quite superior, even to fourth rung functionals, usually better than MP2 and very close to the available CCSD(T) values. [ABSTRACT FROM AUTHOR]

A first (local) bridge between Kohn–Sham density functional theory and the quantum theory of atoms in molecules of Bader is built by means of a second order reduced density gradient expansion of the exchange-correlation energy density at a given bond critical point. This approach leads to the definition of new “mixed” descriptors that are particularly useful for the classification of the chemical interactions for which the traditional atoms in molecules characterization reveals insufficient, as for instance the distinction between hydrogen and agostic bonds. [ABSTRACT FROM AUTHOR]

A comprehensive investigation of one of the basic components of ZnO-based dye-sensitized solar cells (DSSC) is presented, carried out using hybrid density functionals combined to a periodic formalism. Both semiconductor bulk and surfaces are discussed thoroughly, with a particular attention to structural and electronic aspects. Next, three possible adsorption modes of formic acid are compared and discussed at the same level of theory. The results confirm that formic acid appears as a suitable choice for an efficient anchoring of large organic molecules, such as the dyes commonly used for DSSC, to semiconductor surfaces since it allows both a stable adsorption and few but significant contributions to the density of states for all adsorption modes considered. More in general, our results suggest that hybrid functionals and, in particular the parameter free PBE0 (PBE denotes Perdew–Burke–Ernzerhof), can be considered as a reliable tool for modeling complex molecule-semiconductors interfaces such as the one of interest in DSSC, thus providing a powerful computational protocol for the in silico design of new systems for photovoltaic applications. [ABSTRACT FROM AUTHOR]

The first n→π* transitions of 18 nitroso and 16 thiocarbonyl dyes have been computed by time-dependent density functional theory (TD-DFT) using pure as well as global and range-separated hybrid functionals. It turns out that the accuracy of all hybrids is relatively similar, i.e., the inclusion of a growing fraction of exact exchange does neither worsen nor improve significantly the raw TD-DFT estimations. However, after a simple linear regression, it appears that the range-separated hybrids provide a better accuracy than global hybrids. [ABSTRACT FROM AUTHOR]

Using the long-range corrected (LC) density functional theory (DFT) scheme introduced by Iikura et al. [J. Chem. Phys. 115, 3540 (2001)] and the Coulomb-attenuating model (CAM-B3LYP) of Yanai et al. [Chem. Phys. Lett. 393, 51 (2004)], we have calculated the longitudinal dipole moments and static electronic first hyperpolarizabilities of increasingly long polymehtineimine oligomers. For comparison purposes Hartree-Fock (HF), Møller-Plesset perturbation theory (MP2), and conventional pure and hybrid functionals have been considered as well. HF, generalized gradient approximation (GGA), and conventional hybrids provide too large dipole moments for long oligomers, while LC-DFT allows to reduce the discrepancy with respect to MP2 by a factor of 3. For the first hyperpolarizability, the incorrect evolution with the chain length predicted by HF is strongly worsened by BLYP, Perdew-Burke-Ernzerhof (PBE), and also by B3LYP and PBE0. On the reverse, LC-BLYP and LC-PBE hyperpolarizabilities are correctly predicted to be positive (but for the two smallest chains). Indeed, for medium and long oligomers LC hyperpolarizabilities are slightly smaller than MP2 hyperpolarizabilities, as it should be. CAM-B3LYP also strongly improves the B3LYP results, though a bit less impressively for small chain lengths. The present study demonstrates the efficiency of long-range DFT, even in very pathological cases. [ABSTRACT FROM AUTHOR]

The two polymorphs of TiO2, rutile and anatase, have been investigated at the ab initio level using different Hamiltonians with all-electron Gaussian and projector augmented plane wave basis sets. Their equilibrium lattice parameters, relative stabilities, binding energies, and band structures have been evaluated. The calculations have been performed at the Hartree-Fock, density functional theory (DFT), and hybrid (B3LYP and PBE0) levels. As regards DFT, the local density and generalized gradient (PBE) approximations have been used. Our results show an excellent agreement with the experimental band structures and binding energies for the B3LYP and PBE0 functionals, while the best structural descriptions are obtained at the PBE0 level. However, no matter which Hamiltonian and method are used, anatase is found more stable than rutile, in contrast with recent experimental reports, although the relative stabilities of the two phases are very close to each other. Nevertheless, based on the overall results, the hybrid PBE0 functional appears as a good compromise to obtain an accurate description of both structural and electronic properties of solids. [ABSTRACT FROM AUTHOR]

Using the long-range correction (LC) density functional theory (DFT) scheme introduced by Iikura et al. [J. Chem. Phys. 115, 3540 (2001)] and the Coulomb-attenuating model (CAM-B3LYP) of Yanai et al. [Chem. Phys. Lett. 393, 51 (2004)], we have calculated a series of properties that are known to be poorly reproduced by standard functionals: Bond length alternation of π-conjugated polymers, polarizabilities of delocalized chains, and electronic spectra of extended dyes. For each of these properties, we present cases in which traditional hybrid functionals do provide accurate results and cases in which they fail to reproduce the correct trends. The quality of the results is assessed with regard to experimental values and/or data arising from electron-correlated wave function approaches. It turns out that (i) both LC-DFT and CAM-B3LYP provide an accurate bond length alternation for polyacetylene and polymethineimine, although for the latter they decrease slightly too rapidly with chain length. (ii) The LC generalized gradient approximation and MP2 polarizabilities of long polyphosphazene and polymethineimine oligomers agree almost perfectly. In the same way, CAM-B3LYP corrects the major part of the B3LYP faults. (iii) LC and CAM techniques do not help in correcting the nonrealistic evolution with chain length of the absorption wavelengths of cyanine derivatives. In addition, though both schemes significantly overestimate the ground to excited state transition energy of substituted anthraquinone dyes, they provide a more consistent picture once a statistical treatment is performed than do traditional hybrid functionals. [ABSTRACT FROM AUTHOR]

The physicochemical properties of two molten salts, namely, KCl and NaCl, have been studied with a molecular-dynamics approach using a density-functional-based tight-binding (DFTB) model. The obtained results have been compared with a number of previously reported simulations, carried out on smaller systems and using classical force-field techniques. A good agreement has been found for both structural parameters and macroscopic properties, such as self-diffusion coefficients. Furthermore, our DFTB results are very close to the available experimental data. From a more general point of view, our results demonstrate the applicability of DFTB as an efficient tool in the modeling of melts. At the same time, the quality of the obtained results supports the use of this as a reliable alternative to the more expensive ab initio dynamics approaches, if accurate parameters are provided. [ABSTRACT FROM AUTHOR]

An integrated quantum mechanical approach for the structural and magnetic characterization of flexible free radicals in solution has been applied to a model of the glycyl radical engaged in peptidic chains. The hyperfine couplings computed using hybrid density functionals and purposely tailored basis sets are in good agreement with experiment when vibrational averaging effects from low frequency motions and solvent effects (both direct H bonding and bulk) are taken into the proper account. The g tensor shows a smaller dependence on the specific form of the density functional, the extension of the basis set over a standard double-ζ+polarization level, vibrational averaging, and bulk solvent effects. However, hydrogen bridges with solvent molecules belonging to the first solvation shell play a significant role. Together with their intrinsic interest, our results show that a comprehensive and reliable computational approach is becoming available for the complete characterization of open-shell systems of biological interest in their natural environment. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The performance of some kinetic energy density (τ) dependent functionals in predicting the effective Heisenberg exchange has been explored using the KNiF[sub 3] and K[sub 2]NiF[sub 4] insulators as case examples. Our results show that this new generation of functionals represents an important improvement with respect to the current local and gradient corrected functionals yielding a semi-quantitative description of the antiferromagnetic coupling without the need of hybrid approaches thus avoiding the calculation of exact, Hartree–Fock exchange. This feature opens a wide field of application especially in solid state. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In the present paper, we validate and assess a correlation functional based on the so-called meta generalized gradient approximation, whose form and parameters are entirely derived only from first-principles criteria. In particular, we have carried out a detailed comparison with the most common, parametrized correlation functionals. Next, we propose a new model in which the correlation functional proposed by Kriger, Chen, Iafrate, and Savin is integrated in a hybrid Hartree-Fock/density functional theory scheme. In such approach only one, or two in the G2-optimized version, parameters are adjusted on experimental data, all the others being derived from purely theoretical considerations. The results obtained for a set of molecular properties, including H-bonded complexes, proton transfer model, S[sub N]2 reaction and magnetic properties, are satisfactory and comparable, if not better, with those delivered by the most common functionals including heavy parametrization. The way in which the whole functional is derived and the few empirical parameters used make the new exchange-correlation functional widely applicable. [ABSTRACT FROM AUTHOR]

In this paper we propose a modification of the exchange functional introduced by Perdew, Burke, and Ernzerhof, which significantly enlarges the original field of applications. This modification is obtained by a series expansion of the functional, which introduces one additional parameter, but retains all the asymptotic and scaling properties of the original model. The results obtained for structural, thermodynamic, kinetic, and spectroscopic properties are satisfactory and not far from those delivered by the most reliable functionals including heavy parametrization. The way in which the functional is derived and the lack of empirical parameters fitted to specific properties makes the new exchange functional widely applicable, for both quantum chemistry and for condensed-matter physics. [ABSTRACT FROM AUTHOR]

Presents an analysis of the performances of a parameter free density functional model (PBE0) obtained combining the PBE generalized gradient functional with a predefined amount of exact change. Results obtained for structural, thermodynamic, kinetic and spectroscopic properties; Kohn-Sham approach to density function (DF) theory; Systems containing heavier atoms.

The results of a systematic density functional study, carried out using a self-consistent hybrid approach including exact exchange contribution, on the all monocarbonyls of first-row transition metals, are reported. Geometries, harmonic wave numbers, and binding energies, obtained using both standard generalized gradient corrected and hybrid functionals, are compared with previous published theoretical data and the available experimental findings. It is shown that hybrid functionals give results close to highly correlated post Hartree–Fock approaches and which are sensibly different from those obtained by standard local, even gradient corrected, methods. A nice agreement has been also found between theoretical and experimental binding energies. A natural bond orbital analysis confirms the role of the π interaction in the metal-carbonyl bond and gives an explanation to the preference for bent structures found in chromium and copper monocarbonyls. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Extensive density functional calculations are reported for the geometrical structures, thermochemistry, infrared, and hyperfine parameters of representative carbon-centered π radicals. Local functionals can be considered sufficient for geometrical and vibrational parameters, but seriously fail in the computation of thermochemical data and of spin-dependent properties. Gradient corrections (especially Becke exchange and Lee–Yang–Parr correlation functionals) sensibly improve matters. Inclusion of some Hartree–Fock exchange in a fully self-consistent density functional implementation delivers a further significant improvement, approaching the accuracy of the most refined post Hartree–Fock computations. Purposely tailored basis sets are also introduced which are small enough to be used in molecular computations, but still give high quality geometries and hyperfine coupling constants. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Density functional calculations with large basis sets have been performed for nine conformers of neutral glycine. The results obtained by standard, even gradient corrected functionals are significantly different from the best post-Hartree–Fock computations and the available experimental data. Inclusion of some Hartree–Fock exchange significantly improves matters, thus providing a promising protocol for the study of noncovalent interactions in biomolecules. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines exchange functionals with improved long-range behavior and adiabatic connection methods without adjustable parameters. Gradient regions in van der Waals interactions; Details on the Perdew and Wang model of exchange functional modification; Role of exact and density functional exchange in adiabatic connection.

We provide a rationale for a new class of double-hybrid approximations introduced by Brémond and Adamo [J. Chem. Phys. 135, 024106 (2011)] which combine an exchange-correlation density functional with Hartree-Fock exchange weighted by λ and second-order Mo\ller-Plesset (MP2) correlation weighted by λ3. We show that this double-hybrid model can be understood in the context of the density-scaled double-hybrid model proposed by Sharkas et al. [J. Chem. Phys. 134, 064113 (2011)], as approximating the density-scaled correlation functional Ec[n1/λ] by a linear function of λ, interpolating between MP2 at λ = 0 and a density-functional approximation at λ = 1. Numerical results obtained with the Perdew-Burke-Ernzerhof density functional confirms the relevance of this double-hybrid model. [ABSTRACT FROM AUTHOR]

We study the orbital-dependence of three (parameter-free) double-hybrid density functionals, namely the PBE0-DH, the PBE-QIDH models, and the SOS1-PBE-QIDH spin-opposite-scaled variant of the latter. To do it, we feed all their energy terms with different sets of orbitals obtained previously from self-consistent density functional theory calculations using several exchange-correlation functionals (e.g., PBE, PBE0, PBEH&H), or directly with HF-PBE orbitals, to see their effect on selected datasets for atomization and reaction energies, the latter proned to marked self-interaction errors. We find that the PBE-QIDH double-hybrid model shows a great consistency, as the best results are always obtained for the set of orbitals corresponding to its hybrid scheme, which prompts us to recommend this model without any other fitting or reparameterization. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The performances, in the description of excited state potential energy surfaces, of several density functional approximations representative of the currently most applied exchange correlation functionals' families have been tested with respect to post Hartree-Fock references (here Symmetry Adapted Cluster-Configuration Interaction results). An experimentally well-characterized intermolecular proton transfer reaction has been considered as test case. The computed potential energy profiles were analyzed both in the gas phase and in toluene solution, here represented as a polarizable continuum model. The presence of intermolecular (dark) and intramolecular (bright) charge transfer excited states, whose polarity strongly differs along the reaction pathway, makes clear that only subtle compensation between spurious electronic effects-related to the incorrect asymptotic behavior of the functional-and solvent stabilization of polar states leads to the overall correct description of this excited state reaction when using global hybrids with low percentage of Hartree Fock exchange. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The computationally assisted, accelerated design of inorganic functional materials often relies on the ability of a given electronic structure method to return the correct electronic ground state of the material in question. Outlining difficulties with current density functionals and wave function-based approaches, we highlight why double hybrid density functionals represent promising candidates for this purpose. In turn, we show that PBE0-DH (and PBE-QIDH) offers a significant improvement over its hybrid parent functional PBE0 [as well as B3LYP* and coupled cluster singles and doubles with perturbative triples (CCSD(T))] when computing spin-state splitting energies, using high-level diffusion Monte Carlo calculations as a reference. We refer to the opposing influence of Hartree-Fock (HF) exchange and MP2, which permits higher levels of HF exchange and a concomitant reduction in electronic density error, as the reason for the improved performance of double-hybrid functionals relative to hybrid functionals. Additionally, using 16 transition metal (Fe and Co) complexes, we show that low-spin states are stabilised by increasing contributions from MP2 within the double hybrid formulation. Furthermore, this stabilisation effect is more prominent for high field strength ligands than low field strength ligands. [ABSTRACT FROM AUTHOR]

We have computed, at the time-department density functional theory, TD-DFT level of approximation, the ground- and excited-state properties of three typical chromophores, namely indole, coumarin, and benzofurazan, using six functionals (B3LYP, B3P86, PBE0, BMK, BH&HLYP, and CAM-B3LYP) and four atomic basis sets (BSs), the larger being 6-311++G(2d,2p). It turned out that diffuse functions are necessary to obtain correct vertical transition energies. The selected functional mainly impacts on these energies, but the differences of vibrational energies between the ground- and excited-states are almost BS and functional independent. The adiabatic gap estimated with total energies or with Gibbs free enthalpies are nearly the same provided the ZPVE effects are accounted for. Int J Quantum Chem, 2012. © 2012 Wiley Periodicals, Inc. [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]

Using time-dependent density functional theory and the polarizable continuum model, we have simulated the absorption spectra of an extended series of azobenzene dyes. First, we have determined a theoretical level optimal for this important class of dyes, and it turned out that a C-PCM-CAM-B3LYP/6-311+G(d,p)//C-PCM-B3LYP/6-311G(d,p) approach represents an effective compromise between chemical accuracy and computational cost. In a second stage, we have compared the theoretical and experimental transition energies for 46 n → π☆ and 141 π → π☆ excitations. For the full set, that spans over a 302-565 nm domain, we obtained a mean absolute deviation of 13 nm (0.10 eV) and a linear correlation coefficient of 0.95, illustrating the accuracy of our approach, though some significant outliers pertained. In a last step, the impact of several modifications, that is, trans/cis isomerization, variation of the acidity of the medium and azo/hydrazo tautomerism have been modeled with two functionals. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

The molecular structures of 77 nitroaromatic compounds have been correlated to their thermal stabilities by combining the quantitative structure-property relationship (QSPR) method with density functional theory (DFT). More than 300 descriptors (constitutional, topological, geometrical and quantum chemical) have been calculated, and multilinear regressions have been performed to find accurate quantitative relationships with experimental heats of decomposition (−Δ H). In particular, this work demonstrates the importance of accounting for chemical mechanisms during the selection of an adequate experimental data set. A reliable QSPR model that presents a strong correlation with experimental data for both the training and the validation molecular sets ( R = 0.90 and 0.84, respectively) was developed for non-ortho-substituted nitroaromatic compounds. Moreover, its applicability domain was determined, and the model's predictivity reached 0.86 within this applicability domain. To our knowledge, this work has produced the first QSPR model, developed according to the OECD principles of regulatory acceptability, for predicting the thermal stabilities of energetic compounds. [ABSTRACT FROM AUTHOR]

We present a periodic density functional theory investigation of twoproton-ordered phases of ice. Their equilibrium lattice parameters,relative stabilities, formation energies, and densities of states havebeen evaluated. Nine exchange-correlation functionals, representativeof the generalized gradient approximation (GGA), global hybrids,range-separated hybrids, meta-GGA, and hybrid meta-GGA families havebeen taken into account, considering two oxygen basis sets. Althoughthe hydrogen-bond network of ice is well reproduced at the B3LYP,M06-L, or LC- wPBE levels, formation energies are only correctlyevaluated with the two former functionals. Band gaps on the other handare only quantitatively reproduced at the B3LYP level. These resultsindicate that this last functional, a de facto reference formolecular calculations, gives in average the most accurate results forthe considered ice properties. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011 [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]

In this article, we have assessed the performances of some recently proposed density functionals for the prediction of reaction energies involving radicals, notably bond dissociations of small organic molecules or of TEMPO-based ones, and β-scissions, focusing on our TCA family and on range-separated hybrids. It is found that no functional belonging to these two families is able to compete with the M0x one. We have tried to improve the performances of the range-separated hybrids by the optimization of the attenuation parameter, but the improvements for one dataset lead to an unavoidable deterioration for the others. Furthermore, the differences between two different approaches to the long-range/short-range separation are discussed in terms of average enhancement factors, emphasizing the crucial choice of the approximate scheme used for the short-range part. Finally, the influence of the geometries has been considered and found to be negligible for this kind of molecular sets, validating the usual single point energies strategies developed in such benchmarking assessments. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

We use a time-dependent density functional theory approach to investigate the absorption spectra of a panel of organic dyes synthesised and characterised during 2009. Several chemical modifications (solid-state packing, oxidation, variation of acidity...) are tackled, and both successes and failures of theory are highlighted and discussed. The obtained deviations are compared to the errors reported previously for traditional families of organic dyes. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Abstract: The three acid dissociation constants (pK as) of the 8-hydroxyquinoline-5-sulfonic acid were computed using a computational protocol based on Density Functional Theory. A hybrid exchange correlation functional was applied and bulk solvent effects were treated within the framework of the Polarizable Continuum Model. Direct solute–solvent interactions were taken into account adding explicit water molecules. The computed pK as are in line with the experimental data and allow better defining the first pK a, confirmed to be negative. From the calculated pK as, ‘ab initio’ distribution diagrams of the relative concentration of the different species in solution as a function of pH were drawn. [Copyright &y& Elsevier]

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]

In many theoretical studies dealing with the selective complexation of trivalent actinides with respect to trivalent lanthanides, the method of calculation is assessed by comparing computed geometries with crystal structures that are often available. Yet, the selectivity is better rationalized through thermodynamic data, as enthalpy and entropy terms. In this article, we have theoretically modeled competing complexation reactions of [Ce(terpy)3]3+, [U(terpy)3]3+, [Ce(MeBTP)3]3+ and [U(MeBTP)3]3+ systems (terpy = 2,2′:6′2″-terpyridine; MeBTP = methyl-2,6-di(1,2,4-triazin-3-yl)pyridine) within the framework of the Density Functional Theory. Our calculations manage to qualitatively account for the experimental relative stabilities of terpy and MeBTP complexes, and in particular for the better coordinating strength of MeBTP for trivalent uranium. We also show by comparing the MeBTP ligand with its non-alkylated form (HBTP) that model systems often used in quantum chemistry must be carefully chosen when energetic comparisons are undertaken. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic shielding constants of the permanganate ion were computed by the means of density functional theory both from static and dynamic simulations. The hybrid PBE0 exchange correlation functional was used for the determination of structural and magnetic properties. Ab-initio molecular dynamic simulations were performed at the same level of theory using the atom-centred density matrix propagation (ADMP) method. With the aim of understanding the role of coupling of different vibrations, the results obtained at static level and as average along large amplitude motions representing each of the normal modes of the ion were compared to those resulting from dynamic approaches. [Copyright &y& Elsevier]

Corrections to the self-interaction error which is rooted in all standard exchange-correlation functionals in the density functional theory (DFT) have become the object of an increasing interest. After an introduction reminding the origin of the self-interaction error in the DFT formalism, and a brief review of the self-interaction free approximations, we present a simple, yet effective, self-consistent method to correct this error. The model is based on an average density self-interaction correction (ADSIC), where both exchange and Coulomb contributions are screened by a fraction of the electron density. The ansatz on which the method is built makes it particularly appealing, due to its simplicity and its favorable scaling with the size of the system. We have tested the ADSIC approach on one of the classical pathological problem for density functional theory: the direct estimation of the ionization potential from orbital eigenvalues. A large set of different chemical systems, ranging from simple atoms to large fullerenes, has been considered as test cases. Our results show that the ADSIC approach provides good numerical values for all the molecular systems, the agreement with the experimental values increasing, due to its average ansatz, with the size (conjugation) of the systems. [Copyright &y& Elsevier]

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]

In this Letter we propose a new hybrid exchange–correlation functional, in which a recently developed exchange (mPBE) and a meta-GGA correlation (KCIS) are integrated in a hybrid Hartree–Fock/Density Functional Theory scheme. In such approach only one, or two in the G2-optimized version, parameters are adjusted on experimental data, all the others being derived from purely theoretical considerations. The results obtained for a set of molecular properties, including van der Waals and H-bonded complexes, are satisfactory and not far from those delivered by the most reliable functionals including heavy parameterization. The way in which the functional is derived and the few empirical parameters used make the new exchange–correlational functional widely applicable. [Copyright &y& Elsevier]

We present a systematic investigation on the optimized geometric parameters for covalently bonded molecules, nonbonded intermolecular complexes, and transition state structures from three PBE (Perdew-Burke-Ernzerhof)-based doubly hybrid (DH) density functionals, namely PBE0-DH, PBE0-2, and xDH-PBE0. While the former two are the B2PLYP-type of DH functionals with no fit parameters, the latter is the XYG3-type of DH functional (xDH for short) with three fit parameters, whose energy expression is constructed by using density and orbital information from another standard (general) Kohn-Sham functional (i.e., PBE0) for doing the self-consistent field calculations. Generally good performances have been obtained with all three DH functionals, in particular, with xDH-PBE0. [ABSTRACT FROM AUTHOR]

We analyze the performances of the parameter-free hybrid density functional PBE0-1/3 obtained combining the PBE generalized-gradient functional with a predefined amount of exact exchange of 1/3, as recently discussed by Cortona [J. Chem. Phys. 136, 086101 (2012)]. The numerical results that we have obtained for various properties, such as atomization energies (G2-148 dataset), weak interactions (NCB31 dataset), hydrogen-bond length optimizations, and dissociation energies (HB10 dataset), and vertical excitation energies, show an increased performance of PBE0-1/3 with respect to the widely used PBE0. We therefore propose to use one third as the mixing coefficient for the PBE-based hybrid functional. [ABSTRACT FROM AUTHOR]