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Fast electrostatic calculations in energy analysis : method development, applications in investigating organic and organometalic crystals, and to protein/ligand complexes

Abstract : One usually considers the electrostatic nature of atoms to explore intermolecular interactions. The Hansen-Coppens multipolar model is widely used to bring a detailed view of electron distribution on an atomic scale. It is thus a common starting point to investigate chemical behaviour of selected systems, giving access to microscopic insights that elucidate material properties on the large scale.One such property is the electrostatic interaction energy, which tells how strongly two charges attract or repel each other. The multipolar model brings forward a clear picture of charge distributions inside molecules, so a calculation of electrostatic energy based on it provides a better estimate than by using traditional methods (simplifications like point charges). The methods already exist to calculate electrostatic interaction energy, but their weak point is that they take their time to calculate the underlying integrals.The method discussed in this thesis (analytical exact potential / pseudo-multipolar moments, aEP/pMM) replaces the slow numerical integration inherent to the older method with analytical integration. It was integrated in the program Charger. The boost of speed comes from replacing a 3D cubature with a one-dimensional integral, due to favourable mathematical properties of the underlying multipolar model. The improvement in speed goes from 4 to 200 times, and the resulting energies are almost indistinguishable from those obtained by the older method.The goal was also to see how wide one can cast the net of this new Charger approach. It was tested on protein/ligand complexes, organic molecules and metal-organic complexes involving many elements of the first three rows in the periodic table. It was also applied on an organometallic complex containing nickel atoms in its core. In all of these applications, Charger reigned supreme over the old approach in terms of computational time, while guarding exceptional accuracy.The application on the protein/ligand complex pointed to residues which are the major contributors and detractors to ligand binding. It also revealed a possible mutation candidate that could show the predictive power of the Charger approach. The metal-organic complex contained a peculiar contact: Charger helped to characterise it. Charger also unveiled the electrostatic energy of crystal packing for an organic and an organometallic compound. The author hopes that the new aEP/pMM approach will encounter a positive reception and contribute to many an interesting finding across various fields that rely on molecular modeling.
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Submitted on : Wednesday, November 10, 2021 - 9:28:58 AM
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Vedran Vuković. Fast electrostatic calculations in energy analysis : method development, applications in investigating organic and organometalic crystals, and to protein/ligand complexes. Physics [physics]. Université de Lorraine, 2021. English. ⟨NNT : 2021LORR0163⟩. ⟨tel-03423337⟩

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