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Wave function theory (WFT) and density functional theory (DFT)—the two most popular solutions to electronic structure problems of atoms and molecules—share the same origin, dealing with the same subject yet using distinct methodologies. For example, molecular orbitals are artifacts in WFT, whereas in DFT, electron density plays the dominant role. One question that needs to be addressed when using these approaches to appreciate properties related to molecular structure and reactivity is if there is any link between the two. In this work, we present a piece of strong evidence addressing that very question. Using five polymeric systems as illustrative examples, we reveal that using quantities from DFT such as Shannon entropy, Fisher information, Ghosh-Berkowitz-Parr entropy, Onicescu information energy, Rényi entropy, etc., one is able to accurately evaluate orbital-related properties in WFT like frontier orbital energies and the HOMO (highest occupied molecular orbital)/LUMO (lowest unoccupied molecular orbital) gap. We verified these results at both the whole molecule level and the atoms-in-molecules level. These results provide compelling evidence suggesting that WFT and DFT are complementary to each other, both trying to comprehend the same properties of the electronic structure and molecular reactivity from different perspectives using their own characteristic vocabulary. Hence, there should be a bridge or bridges between the two approaches.

The factors that explain the competition between intramolecular NO linkage photoisomerization and NO photorelease in five ruthenium nitrosyl complexes were investigated. By applying DFT-based methods, it was possible to characterize the ground states and lowest triplet potential energy surfaces of these species, and to establish that both photoisomerization and photorelease processes can occur in the lowest triplet state of each species. This work highlights the crucial role of the sideways-bonded isomer, a metastable state also known as the MS2 isomer, in the photochemical loss of NO, while the results obtained also indicate that the population of the triplet state of this isomer is compulsory for both processes and show how photoisomerization and photorelease interfere. Graphical Abstract Illustration of the crucial role of the 3 MS2 state in the photoreactivities of ruthenium nitrosyl complexes

The overall objective was to identify an accurate computational electronic method to virtually screen phenolic compounds through their antioxidant and free-radical scavenging activity. The impact of a key parameter of the density functional theory (DFT) approach was studied. Performances of the 21 most commonly used exchange-correlation functionals are thus detailed in the evaluation of the main energetic parameters related to the activities of two prototype antioxidants, namely quercetin and edaravone, is reported. These functionals have been chosen among those belonging to three different families of hybrid functionals, namely global, range separated, and double hybrids. Other computational parameters have also been considered, such as basis set and solvent effects. The selected parameters, namely bond dissociation enthalpy (BDE), ionization potential (IP), and proton dissociation enthalpy (PDE) allow a mechanistic evaluation of the antioxidant activities of free radical scavengers. Our results show that all the selected functionals provide a coherent picture of these properties, predicting the same order of BDEs and PDEs. However, with respect to the reference values, the errors found at CBS-Q3 level significantly vary with the functional. Although it is difficult to evidence a global trend from the reported data, it clearly appears that LC-ωPBE, M05-2X, and M06-2X are the most suitable approaches for the considered properties, giving the lowest cumulative mean absolute errors. These methods are therefore suggested for an accurate and fast evaluation of energetic parameters related to an antioxidant activity via free radical scavenging.

Anthelmintic praziquantel (PZQ) and its molecular and crystal lattice structures were studied by means of atomistic calculations based on empirical interatomic potentials and quantum mechanical methods (DFT). This chiral drug presents several crystal polymorphs due to the enantiomers (either R or S) or the racemic crystal, and different molecular conformations. The relative configurations of the carbonyl groups in PZQ define these conformations that produce different polymorphs. The polarity of these conformers is quite different and their relative population can vary in media with different polarity. Crystal structures of PZQ were studied by infrared and Raman spectroscopy and their spectroscopical properties were calculated by quantum mechanical methods, assigning many of their bands, and finding a good agreement with experimental data.

To limit in vivo experiments, the use of quantitative structure-activity relationships (QSARs) is advocated by REACH regulation to predict the required fish, invertebrate, and algae EC50 for chemical registration. The aim of this work was to develop reliable QSARs in order to model both invertebrate and algae EC50 for organic solvents, regardless of the mechanism of toxic action involved. EC50 represents the concentration producing the 50 % immobilization of invertebrates or the 50 % growth inhibition of algae. The dataset was composed of 122 organic solvents chemically heterogeneous which were characterized by their invertebrate and/or algae EC50. These solvents were described by physico-chemical descriptors and quantum theoretical parameters calculated via density functional theory. QSAR models were developed by multiple linear regression using the ordinary least squares method and descriptor selection was performed by the Kubinyi function. Invertebrate EC50 was well-described with LogP, dielectric constant, surface tension, and minimal atomic Mulliken charges while algae EC50 of organic solvents (except amines) was predicted with LogP and LUMO energy. To evaluate robustness and predictive performance of the QSARs developed, several strategies have been used to select solvent training sets (random, EC50-based selection and a space-filling design) and both internal and external validations were performed.

Understanding the interaction between graphene and polymers is of essential interest when designing novel nanocomposites with reinforced mechanical and electrical properties. In this computational study, the interaction of pristine graphene (PG) and graphene oxide (GO) with a series of functional groups, representative of the functionalised buildings blocks occurring in different polymers, and attached to aliphatic and aromatic chains, is analyzed using dispersion-corrected semi-empirical methods (PM6-D3H4X) and density functional theory calculations with empirical dispersion corrections. Functional groups include alkyl, hydroxyl, aldehyde, carboxyl, amino and nitro groups, and the binding energies of these groups with graphene derivatives (PG and GO) are determined. Nitro- and carbonyl groups display stronger interactions in both aliphatic and aromatic chains. The importance of dispersion-type and non-covalent interactions (NCI) in general, which typically, double the interaction energies, is revealed. The results are interpreted in an extensive NCI analysis in order to characterize the different types of NCI, providing a better understanding of the nature of the interaction (π–π stacking, CH–π bonding, H-bonding and lone pair–π interaction) at stake. In order to highlight the influence of polymer structure/conformation on top of that of their functional groups, the binding of three polymers, polyethylene (PE), polystyrene (PS) and polyvinylidene fluoride (PVDF), on pristine graphene is also investigated. Our calculations indicate that, although all polymers exhibit evident attractive interactions with the graphene sheet, the overall interaction is strongly influenced by the specific polymer structure. Thus, three main conformations of PVDF (the so-called α, β and γ, ε conformations) are analyzed and we find that, although the α-conformer with a trans-gauche-trans-gauche (TGTG’) conformation is the lowest energy conformer, the β-conformation of PVDF with the hydrogen atoms facing the graphene (“F-up”) has the strongest interaction with the graphene surface among the polymers under consideration. Taken together, our computational approach sheds light on the character and importance of non-covalent graphene-polymer functional group interactions combined with the structural/conformational properties of the polymer, which are at stake in the design of novel nanocomposites with reinforced mechanical and electrical properties.

The net charge transfer process that occurs between two species, A and B, interacting with each other, may be decomposed into two processes: one in which A receives charge from B, which can be identified as the electrophilic channel for A or the nucleophilic channel for B, and a second in which A donates charge to B, which can be identified as the nucleophilic channel for A or the electrophilic channel for B. By determining the amount of charge associated with both processes through the minimization of the interaction energy associated with each case, the expressions for the amount of charge involved in each case can be expressed in terms of the directional chemical potentials and the hardnesses of the interacting species. The correlation between the charges obtained for the interaction between phosphine ligands of the type PRR'R'' and Ni, and the A 1 carbonyl stretching frequency provides support for their interpretation as measures of the electrophilicity and nucleophilicity of a chemical species, and, at the same time, allows one to describe the donation and back-donation processes in terms of the density functional theory of chemical reactivity.

It has been overlooked that the change of hardness, η , upon bonding is intimately connected to thermochemical cycles, which determine whether hardness is increased according to Pearson’s “maximum hardness principle” (MHP) or equalized, as expected by Datta’s “hardness equalization principle” (HEP). So far the performances of these likely incompatible “structural principles” have not been compared. Computational validations have been inconclusive because the hardness values and even their qualitative trends change drastically and unsystematically at different levels of theory. Here I elucidate the physical basis of both rules, and shed new light on them from an elementary experimental source. The difference, Δ η  =  η mol – < η at >, of the molecular hardness, η mol , and the averaged atomic hardness, < η at >, is determined by thermochemical cycles involving the bond dissociation energies D of the molecule, D + of its cation, and D − of its anion. Whether the hardness is increased, equalized or even reduced is strongly influenced by Δ D =  2 D – D +   − D − . Quantitative expressions for Δ η are obtained, and the principles are tested on 90 molecules and the association reactions forming them. The Wigner-Witmer symmetry constraints on bonding require the valence state (VS) hardness, η VS , instead of the conventional ground state (GS) hardness, η GS . Many intriguingly “unpredictable” failures and systematic shortcomings of said “principles” are understood and overcome for the first time, including failures involving exotic and/or challenging molecules, such as Be 2, B 2 , O 3 , and transition metal compounds. New linear relationships are discovered between the MHP hardness increase Δ η VS and the intrinsic bond dissociation energy D i . For bond formations, MHP and HEP are not compatible, and HEP does not qualify as an ordering rule.

A first-principle investigation of structures and properties of Ni n Pd n (n=1-5) clusters is presented. For this study, the linear combination of Gaussian-type orbitals auxiliary density functional theory (LCGTO-ADFT) method has been employed. In order to determine the lowest energy structures, several isomers in different spin multiplicities were studied, for each cluster size. Initial structures, for which successive geometry optimization was computed without any constrain, were taken along Born–Oppenheimer molecular dynamics (BOMD) trajectories. To discriminate between minima and transition state structures, harmonic frequency analyses were performed at the optimized structures. Ground state structures, bond lengths, harmonic frequencies, dissociation energy, ionization potential, electron affinity and spin density plots are presented. This work demonstrates, that the Pd atoms prefer to allocate on the surface of the cluster structures whose core is formed by the 3d TM atoms type. Moreover, it has been observed that the ground-state structure spin multiplicity increases as the system size grows. The results of this study contribute to gain insight into how structures and energy properties change with cluster size in bimetallic Pd-based alloys.

The regioselectivity of the 1,3-dipolar cycloaddition of a model nitrone with a set of dipolarophiles, presenting diverse electronic effects, is analyzed using conceptual density functional theory (DFT) methods. We deviate from standard approaches based on frontier molecular orbitals and formulations of the local hard/soft acid/base principle and use instead the dual descriptor. A detailed analysis is carried out to determine the influence of the way to calculate the dual descriptor, the computational procedure, basis set and choice of method to condensate the values of this descriptor. We show that the qualitative regioselectivity predictions depend on the choice of “computational conditions”, something that indicates the danger of using black-box computational set-ups in conceptual DFT studies.