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Some of the simple prototype molecular systems are evaluated to study the response of the global and local reactivity density-based descriptors namely Fukui function, local softness, hardness and chemical potential in the presence of external electric field. It is demonstrated that the increase in the value of hardness in the presence of electric field does not necessarily imply that the reactivity of the molecular systems would be lowered or vice versa.

Investigation reveals that the Al4 unit in neutral Al4Na4 and anion Al4Na3 (super -) clusters has 4n Pi electrons and has a rectangular structure with alternate Pi bonds. Neutral Al4Na4 and anion Al4Na3 (super -) clusters satisfy the criteria for antiaromaticity and are metallo-antiaromatic compounds.

The steadiness of Lewis acid-base complexes using the hard-soft acid-base (HSAB) technique is discussed. The major function of the electronegativity equalization and the charge redistribution process in stabilizing the complexes is established.

An examination is done on the density functional theory (DFT) descriptors, which have been used to explain 'intermolecular' reactivity. The concept of group softness is seen to be efficient for both types of charge partitioning used and all of the basis sets used for the research.

Research was conducted to examine the impact of isomorphous substitution of Si by Al, Ga and B in the tetrahedral sites of a zeolite framework on the characteristics of Bronsted acid sites using computational methods. The density functional theory based acidity descriptor 'local softness' and a new acidity descriptor 'relative electrophilicity' were used to predict the acidity sequence of the zeolite clusters. Results demonstrate that the acidity trend obtained from the relative electrophilicity follows the experimental trend.

Local reactivity descriptions, such as the condensed local softness and Fukui function, are employed to investigate the intercluster reactivity of the metalloatomatic [Al4Li(super -) and Al4Na(super -)] and antiaromatic (AL4Li4 and Al4Na4) compounds. It is believed that the formation of the AL4Li(super -) type of metalloaromatic clusters would be responsible for the increase in the efficiency of the electron injection of the Al-Li cathode.

The behavior of local reactivity descriptors such as condensed fukui functions, 'relative electrophilicity' and 'relative nucleophilicity' is studied as the complexation reaction of BH3 or fluoroboranes and NH3 proceeds. The change of these descriptors of different atoms during the reaction is highlighted.

A critical study on the applicability and reliability of the semiquantitative model based on the local hard-soft acid-base principle in calculating the interaction energy for the intermolecular interactions were performed. The effects of basis sets, electron correlation, and electron partitioning methods on the calculation of IE of the complexes using global and local reactivity descriptors were also studied.

Studies conducted to examine the local hard-soft acid-base (HSAB) principle for describing multiple-site interactions between the molecular systems are discussed. A detailed study on model prototype interactions that are relevant to biological molecular interaction processes is presented.

Metalclusters of silver have attracted recent interest of researchersas a result of their potential in different catalytic applicationsand low cost. However, due to the completely filled d orbital andvery high first ionization potential of the silver atom, the silver-basedcatalysts interact very weakly with the reacting molecules. In thecurrent work, density functional theory calculations were carriedout to investigate the effect of hydrogen atom chemisorption on thereactivity and catalytic properties of inert silver clusters. Ourresults affirm that the hydrogen atom chemisorption leads to enhancementin the binding energy of the adsorbed O2molecule on theinert silver clusters. The increase in the binding energy is alsocharacterized by the decrease in the Ag–O and increase in theO–O bond lengths in the case of the AgnH silver clusters. Pertinent to the increase in the O–Obond length, a significant red shift in the O–O stretchingfrequency is also noted in the case of the AgnH silver clusters. Moreover, the hydrogen atom chemisorbedsilver clusters show low reaction barriers and high heat of formationof the final products for the environmentally important CO oxidationreaction as compared to the parent catalytically inactive clusters.The obtained results were compared with those of the correspondinggold and hydrogen atom chemisorbed gold clusters obtained at the samelevel of theory. It is expected the current computational study willprovide key insights for future advances in the design of efficientnanosilver-based catalysts through the adsorption of a small atomor a ligand. [ABSTRACT FROM AUTHOR]

Aluminum clusters are now technologicallyimportant due to theirhigh catalytic activity. Our present study on the small-sized aluminumclusters applies density functional theory (DFT)-based reactivitydescriptors to identify potential sites for adsorption and eventualchemical reaction. Depending on symmetry, susceptibility of varioustype of reactive sites within a cluster toward an impending electrophilicand/or nucleophilic attack is predicted using the reactivity descriptors.In addition, the study devises general rules as to how the size, shape,and charge of the cluster influences the number of available sitesfor an electrophilic and/or nucleophilic attack. The predictions byreactivity descriptors are validated by performing an explicit adsorptionof water molecule on Al clusters with four atoms. The adsorption studiesdemonstrate that the most stable water–cluster complex is obtainedwhen the molecule is adsorbed through an oxygen atom on the site withthe highest relative electrophilicity. [ABSTRACT FROM AUTHOR]

Designing an efficient and cost-effective catalyst for ammonia borane ( AB ) dehydrogenation remains a persistent challenge in advancing a hydrogen-based economy. Transition metal complexes, known for their C-H bond activation capabilities, have emerged as promising candidates for AB dehydrogenation. In this study, we investigated two recently synthesized C-H activation catalysts, 1 (Co IV -dinitrate complex) and 2 (Ni IV -nitrate complex), and demonstrated their efficacy for AB dehydrogenation. Using density functional theory calculations and a detailed analysis, we elucidated the AB dehydrogenation mechanism of these complexes. Our results revealed that both complexes 1 and 2 can efficiently dehydrogenate AB at room temperature, although the abstraction of molecular H 2 from these complexes requires slightly elevated temperatures. We utilized H 2 binding free energy calculations to identify potentially active sites and observed that complex 2 can release two equivalents of H 2 at a temperature slightly higher than room temperature. Furthermore, we investigated AB dehydrogenation kinetics and thermodynamics in iron (Fe)-substituted systems, complexes 3 and 4 . Our results showed that the strategic alteration of the central metal atom, replacing Ni in complex 2 with Fe in complex 4 , resulted in enhanced kinetics and thermodynamics for AB dehydrogenation in the initial cycle. These results underscore the potential of high-valent first-row transition metal complexes for facilitating AB dehydrogenation at room temperature. Additionally, our study highlights the beneficial impact of incorporating iron into such mononuclear systems, enhancing their catalytic activity.

The negative ion resonance states, which are electron-molecule metastable compound states, play the most important role in free-electron controlled molecular reactions and low-energy free-electron-induced DNA damage. Their electronic structure is often only poorly described but crucial to an understanding of their reaction dynamics. One of the most important challenges to current electronic structure theory is the computation of negative ion resonance states. As a major step forward, coupled-cluster theories, which are well-known for their ability to produce the best approximate bound state electronic eigen solutions, are upgraded to offer the most accurate and effective approximations for negative ion resonance states. The existing Fock-space coupled-cluster (FSCC) and the equation-of-motion coupled-cluster (EOM-CC) approaches that compute bound states are redesigned for the direct and simultaneous determination of both the kinetic energy of the free electron at which the electron-molecule compound states are resonantly formed and the corresponding autodetachment decay rate of the electron from the metastable compound state. This Feature Article reviews the computation of negative ion resonances using the FSCC approach and, in passing, provides the highlights of the equivalent EOM-CC approach.

We report a comparative single-reference and multireference coupled-cluster investigation on the structure, potential energy surface, and IR spectroscopic properties of the trans peroxo nitrate radical, one of the key intermediates in stratospheric NOX chemistry. The previous single-reference ab initio studies predicted an unbound structure for the trans peroxo nitrate radical. However, our Fock space multireference coupled-cluster calculation confirms a bound structure for the trans peroxo nitrate radical, in accordance with the experimental results reported earlier. Further, the analysis of the potential energy surface in FSMRCC method indicates a well-behaved minima, contrary to the shallow minima predicted by the single-reference coupled-cluster method. The harmonic force field analysis, of various possible isomers of peroxo nitrate also reveals that only the trans structure leads to the experimentally observed IR peak at 1840 cm(-1). The present study highlights the critical importance of nondynamic correlation in predicting the structure and properties of high-energy stratospheric NOx radicals.

Local hard-soft acid-base (HSAB) principle is semiquantitative in nature due to the presence of an ad hoc charge transfer parameter. The accuracy of HSAB principle significantly depends on the definition of this ad hoc parameter. In this paper, for the first time we have introduced the second-order approximation of ΔN (ΔNsecond) as an ad hoc parameter for charge transfer to calculate interaction energies of multiple site based interactions using local hard soft acid base principle. The second-order approximation of ΔN has been derived from Sanderson's electronegativity equalization principle. To validate our approach, we have studied interaction energies of some prototype molecules. The interaction energies obtained from our approach have been further compared with the interaction energies of those obtained using other charge transfer parameters (ΔNfirst and λ) and the conventional methods. We have also discussed the advantages and limitations of the approach.

A site-selectivity model, based on the Fukui function as a local reactivity descriptor, has been applied to 1,2-disubstituted pyridinium ions incorporating two competing sites of similar reactivity, i.e., 1-methylene and 2-methylene, which may undergo deprotonation depending on the nature of substituent present on these moieties. Applicability of the local HSAB rule, in context with the Li-Evans' generalized HSAB principle suggesting the hard-hard interactions to be controlled by minimum Fukui function, has been illustrated. Global and local reactivity descriptors have been computed by carrying out DFT calculations at B3LYP/6-31++G** level using Mulliken and NPA methods for charge analysis. A comparison with the calculated deprotonation energies involving two sites indicates that the observed site selectivity in differently substituted pyridinium ions is better explained by the Li-Evans rule of minimum Fukui function for hard-hard interactions.