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Chemical Reactivity |
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Chemistry is the science studying the transformation of matter and the properties of matter relevant to it. Being essentially experimental in nature, the advent of quantum mechanics in the early 20th century physics however laid down the basis for the evaluation of these properties from first principles through Schrödinger's wave function based equation. Since this equation cannot be solved analytically for atoms or molecules with two or more electrons, decades were devoted to develop suitable approximation methods (Hückel, Coulson, Fock, Hartree, Mulliken, Roothaan, Parr, Pople, ...), supported from the sixties on by the ongoing and spectacular increase in computer power. The history of Quantum Chemistry, as the new discipline was termed, is a continuing story of approximations of ever increasing sophistication. An important breakthrough was the realisation in 1964 by Kohn and Hohenberg that a much simpler quantity than the wave function, namely the electron density function, can be considered as the information carrier for (the properties of) atoms, molecules, and the solid state. This spectacular result gave birth to the Density Functional Theory (DFT), a technique first used by physicists but in the nineties pervading nearly the complete field of Quantum Chemistry. Moreover DFT provides chemists a firm basis to a series of well-known but rather vaguely defined concepts such as electronegativity, chemical hardness and softness .... offering a first principles interpretation of chemical reactivity. The research themes presented below are to be seen in the context outlined above. - Development and study of density based atomic and molecular properties/descriptors relevant to reactivity: how can the outcome of a reaction be foreseen on the basis of the properties of individual atoms or molecules, partially taking into account some well chosen characteristics of the partner, of the surroundings (solvent, crystal....). Quantifying atomic or molecular similarity deserves particular interest e.g. when comparing reactivity through series of similar molecules, the dissimilarity between enantiomers in chiral systems being a particularly intriguing case. - Establishing analogies between the concepts emerging from DFT and macroscopic thermodynamics for which the analogy between the electronic and macroscopic chemical potential is a well known example. Results from thermodynamics could then be transferred to the electronic level. - Studies of reactions as such, varying from "classical" organic and inorganic reactions to reaction patterns in biochemical systems in which the influence of catalysis may be a common denominator (systems ranging from transition metal complexes to zeolites and enzymes). This part is of direct relevance to the understanding of biochemical reactions and is also of utmost importance for chemical industry. The role of aromaticity and chemical hardness in the catalytic effect will be investigated. A "fil rouge" through this project is the bridge between chemistry and physics: in the theoretical description of matter at the atomic level both disciplines of science often use similar, DFT-based, concepts however within a different formalism and with a different nomenclature, sometimes preventing fruitful discussions between chemists and physicists. Only with a common language optimum conditions are created for solving problems at the intersection of those two disciplines which laid the basis of an understanding of matter and its behavior in various conditions. Associated Research teamsALGC (VUB)
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