Pratim K. Chattaraj

Chemical reactivity theory : a density functional view

How I Came about Working on Conceptual DFT, R.G. Parr Chemical Reactivity Concepts in Density Functional Theory, J.L. Gazquez Quantum Chemistry of Bonding and Interactions, P. Kolandaivel, P. Venuvanalingam, and G.N. Sastry Concepts in Electron Density, B.M. Deb Atoms and Molecules: A Momentum Space Perspective, S.R. Gadre and P. Balanarayan Time-Dependent Density Functional Theory of Many-Electron Systems, S.K. Ghosh Exchange-Correlation Potential of Kohn-Sham Theory A Physical Perspective, M.K. Harbola Time-Dependent Density Functional Theory from a Bohmian Perspective, A.S. Sanz, X. Gimenez, J.M. Bofill, and S. Miret-Artes Time-Independent Theories for a Single Excited State, A. Nagy, M. Levy, and P. Ayers Spin-Polarized Density Functional Theory: Chemical Reactivity, R. Vargas and M. Galvan The Hardness of Closed Systems, R.G. Pearson Fukui Function and Local Softness as Reactivity Descriptors, A.K. Chandra and M.T. Nguyen Electrophilicity, S. Liu Application of Density Functional Theory (DFT) in Organometallic Complexes: A Case Study of Cp2M Fragment (M = Ti, Zr) in C-C Coupling and Decoupling Reactions, S. De and E.D. Jemmis Atoms in Molecules and Population Analysis, P. Bultinck and P. Popelier Molecular Quantum Similarity, P. Bultinck, S. Van Damme, and R. Carbo-Dorca The Electrostatic Potential as a Guide to Molecular Interactive Behavior, P. Politzer and J.S. Murray The Fukui Function, P. Ayers, W. Yang, and L.J. Bartolotti The Shape Function, P. Ayers and A. Cedillo An Introduction to the Electron Localization Function, ELF, P. Fuentealba, D. Guerra, and A. Savin The Reaction Force: A Rigorously- Defined Approach to Analyse Chemical and Physical Process, A. Toro-Labbe, S. Gutierrez-Oliva, P. Politzer, and J.S. Murray Characterization of Changes in Chemical Reactions by Bond Order and Valence Indices, G. Lendvay Variation in Local Reactivity During Molecular Vibrations, Internal Rotations and Chemical Reactions, S. Giri, D.R. Roy, and P.K. Chattaraj Reactivity and Polarisability Responses, P. Senet External Field Effects and Chemical Reactivity, R. Kar and S. Pal Solvent Effects and Chemical Reactivity, V. Subramanian Conceptual Density Functional Theory, Towards an Alternative Understanding of Non-Covalent Interactions, P. Geerlings Aromaticity and Chemical Reactivity, E. Matito, J. Poater, M. Sola, and P.V.R. Schleyer Multifold Aromaticity, Multifold Antiaromaticity and Conflicting Aromaticity Implications for Stability and Reactivity of Clusters, D.Y. Zubarev, A P. Sergeeva, and A.I. Boldyrev Probing the Coupling between Electronic and Geometric Structures of Open and Closed Molecular Systems, R.F. Nalewajski Predicting Chemical Reactivity and Bioactivity of Molecules from Structure, S.C. Basak, D. Mills, R. Natarajan, and B.D. Gute Chemical Reactivity: Industrial Application, A. Chatterjee Electronic Structure of Confined Atoms, J. Garza, R. Vargas, and K.D. Sen Computation of Reactivity Indices: The Integer Discontinuity and Temporary Anions, F. De Proft, and D.J. Tozer

Update 2 of: Electrophilicity Index.

6.1. Molecular Vibrations PR58 6.2. Molecular Internal Rotations PR58 6.3. Chemical Reactions PR58 7. Dynamical Variants PR62 7.1. Quantum Fluid Density Functional Theory PR62 7.2. Atom-Field Interactions PR62 7.3. Ion-Atom Collisions PR62 7.4. Chemical Kinetics PR62 8. Spin Dependent Generalizations PR63 8.1. {N, Ns, v(r b)} Representation PR63 8.2. {NR, N , v(r b)} Representation PR64 9. Conclusions PR65 10. Abbreviations and Symbols of Some Important Subjects/Quantities PR

Variation of the Electrophilicity Index along the Reaction Path

Some exact conditions for the extremals of the electrophilicity index, ω = μ(2)/2η (Parr, R. G.; von Szentpály, L.; Liu, S. J. Am. Chem. Soc. 1999, 121, 1922), along an arbitrary reaction coordinate, have been carefully examined. Implications within the widely used finite difference approximation for the density-functional based reactivity descriptors, their relationship with the maximum hardness principle, and the reliability of the general relationships have been tested in the framework of computational evidence for some simple systems of chemical interest.

THE MAXIMUM HARDNESS PRINCIPLE IN THE GYFTOPOULOS-HATSOPOULOS THREE-LEVEL MODEL FOR AN ATOMIC OR MOLECULAR SPECIES AND ITS POSITIVE AND NEGATIVE IONS

Abstract The maximum hardness principle is examined within the Gyftopoulos-Hatsopoulos three-level model for an electronic system. As an atom or a molecule approaches equilibrium at some chemical potential μ and constant temperature T, its softness (inverse hardness) is shown to most often approach a minimum value.

Hydrogen storage in clathrate hydrates.

Structure, stability, and reactivity of clathrate hydrates with or without hydrogen encapsulation are studied using standard density functional calculations. Conceptual density functional theory based reactivity descriptors and the associated electronic structure principles are used to explain the hydrogen storage properties of clathrate hydrates. Different thermodynamic quantities associated with H(2)-trapping are also computed. The stability of the H(2)-clathrate hydrate complexes increases upon the subsequent addition of hydrogen molecules to the clathrate hydrates. The efficacy of trapping hydrogen molecules inside the cages of clathrate hydrates in an endohedral fashion depends upon the cavity sizes and shapes of the clathrate hydrates. Computational studies reveal that 5(12) and 5(12)6(2) structures are able to accommodate up to two H(2) molecules whereas 5(12)6(8) can accommodate up to six hydrogen molecules. Adsorption and desorption rates conform to that of a good hydrogen storage material.

On the Validity of the Maximum Hardness Principle and the Minimum Electrophilicity Principle during Chemical Reactions

Hardness and electrophilicity values for several molecules involved in different chemical reactions are calculated at various levels of theory and by using different basis sets. Effects of these aspects as well as different approximations to the calculation of those values vis-à-vis the validity of the maximum hardness and minimum electrophilicity principles are analyzed in the cases of some representative reactions. Among 101 studied exothermic reactions, 61.4% and 69.3% of the reactions are found to obey the maximum hardness and minimum electrophilicity principles, respectively, when hardness of products and reactants is expressed in terms of their geometric means. However, when we use arithmetic mean, the percentage reduces to some extent. When we express the hardness in terms of scaled hardness, the percentage obeying maximum hardness principle improves. We have observed that maximum hardness principle is more likely to fail in the cases of very hard species like F(-), H(2), CH(4), N(2), and OH appearing in the reactant side and in most cases of the association reactions. Most of the association reactions obey the minimum electrophilicity principle nicely. The best results (69.3%) for the maximum hardness and minimum electrophilicity principles reject the 50% null hypothesis at the 2% level of significance.

The maximum hardness principle implies the hard/soft acid/base rule

A recent paper [P. W. Ayers, J. Chem. Phys122, 141102 (2005)] considered the hard/soft acid/base exchange reaction, showing that the products associated with the hard/soft acid/base rule (in which the hard acid and hard base are bound, as are the soft acid and soft base) have lower energy than the alternative (in which the hard acid and soft base would have been bound and similarly the soft acid and hard base). Here we show that the maximum hardness principle also predicts this result. Unlike the previous derivation, we do not need to make any assumptions about the relative strength of the acids and bases.

Fukui function from a gradient expansion formula, and estimate of hardness and covalent radius for an atom

The Fukui function for a neutral atom is expressed as its LDA approximation plus a one‐parameter gradient correction, and the resultant formula is numerically tested. Expressing hardness as a density functional involving this Fukui function, global hardness values are determined for several atoms. Estimates also are made of the covalent radii of neutral atoms. Calculated Fukui functions exhibit characteristics similar to those reported in the literature. Calculated hardnesses compare favorably with experimental values, and predicted covalent radii are in agreement with existing theoretical values and experimental data. No information other than the electron densities of the neutral species enter in the calculations. An exact nuclear cusp condition on the Fukui function is derived.

Analyzing toxicity through electrophilicity.

SummaryThe toxicological structure-activity relationships are investigated using conceptual DFT based descriptors like global and local electrophilicities. In the present work the usefulness of electrophilicity in predicting toxicity of several polyaromatic hydrocarbons (PAH) is assessed. The toxicity is expressed through biological activity data (pIC50) defined as molar concentration of those chemicals necessary to displace 50% of radiolabeled tetrachlorodibenzo-p-dioxin (TCDD) from the arylhydrocarbon (Ah) receptor. The experimental toxicity values (pIC50) for the electron acceptor toxin like polychlorinated dibenzofurans (PCDF) are taken as dependent variables and the DFT based global descriptor electrophilicity index (ω) is taken as independent variable in the training set. The same model is then tested on a test set of polychlorinated biphenyls (PCB). A good correlation is obtained which vindicates the importance of these descriptors in the QSAR studies on toxins. These toxins act as electron acceptors in the presence of biomolecules whereas aliphatic amines behave as electron donors some of which are also taken into account for the present work. The toxicity values of the aliphatic amines in terms of the 50% inhibitory growth concentration (IGC50) towards ciliate fresh-water protozoa Tetrahymena pyriformis are considered. Since there is no global nucleophilicity we apply local nucleophilicity (ωmax+) as the descriptor in this case of training set. The same regression model is then applied to a test set of amino alcohols. Although the correlation is very good the statistical analysis reflects some cross validation problem. As a further check the amines and amino alcohols are used together to form both the training and the test sets to provide good correlation. It is demonstrated that the toxicity of several toxins (both electron donors and acceptors) in the gas and solution phases can be adequately explained in terms of global and local electrophilicities. Amount of charge transfer between the toxin and the biosystem, simulated as nucleic acid bases and DNA base pairs, indicates the importance of charge transfer in the observed toxicity. The major strength of the present analysis vis-à-vis the existing ones rests on the fact that it requires only one descriptor having a direct relationship with toxicity to provide a better correlation. Importance of using the information from both the toxin and the biosystem is also analyzed.

Comparison of Global Reactivity Descriptors Calculated Using Various Density Functionals: A QSAR Perspective

Conceptual density functional theory (DFT) based global reactivity descriptors are used to understand the relationship between structure, stability, and global chemical reactivity. Furthermore, these descriptors are employed in the development of quantitative structure-activity (QSAR), structure-property (QSPR), and structure-toxicity (QSTR) relationships. However, the predictive power of various relationships depends on the reliable estimates of these descriptors. The basic working equations used to calculate these descriptors contain both the ionization potential and the electron affinity of chosen molecules. Therefore, efficiency of different density functionals (DFs) in predicting the ionization potential and the electron affinity has to be systematically evaluated. With a view to benchmark the method of calculation of global reactivity descriptors, comprehensive calculations have been carried out on a series of chlorinated benzenes using a variety of density functionals employing different basis sets. In addition, to assess the utility of global reactivity descriptors, the relationships between the reactivity-electrophilicity and the structure-toxicity have been developed. The ionization potential and the electron affinity values obtained from M05-2X method using the ΔSCF approach are closer to the corresponding experimental values. This method reliably predicts these electronic properties when compared to the other DFT methods. The analysis of a series of QSTR equations reveals that computationally economic DFT functionals can be effectively and routinely applied in the development of QSAR/QSPR/QSTR.