Efficient Quantum Chemistry for Applications in Anharmonic Vibrational Analysis and Molecular Crystals
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Nelson, Philip
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Abstract
Quantum chemistry can give invaluable quantitative insights into the properties
of molecular systems without the need for physical experimentation. However,
the poor algorithmic scaling of quantum chemistry methods restricts the most accurate methods to all but the smallest systems. Development of improved software, algorithms, and theoretical approximations can extend the size of molecules able to be studied computationally, an essential prerequisite for applications to real chemical systems.
In the first two chapters, we present open-source software for the computation
of the anharmonic vibrational frequencies of molecules using vibrational
perturbation theory. Through the use of focal-point approximations to estimate
complete-basis coupled cluster and novel software enabling automated distributed
computations, we are able to obtain anharmonic frequencies in a fraction of the time of alternative approaches without sacrificing accuracy. Computation of the
lattice energies of molecular crystals is another challenging application of
quantum chemistry methods. Chapter 4 explores the contributions of three-body
interactions in crystalline formamide, acetic acid, and imidazole. We
demonstrate the ability to obtain three-body contributions to the lattice energy
of molecular crystals at accuracy within 1 kJ/mol at a greatly reduced
compuational cost, using approximate methods and geometric screening of the
many-body expansion. Finally, we present results of a preliminary study of
virtual screening for G-protein coupled receptor targets, an important class of
pharmaceutically relevant proteins, using machine learning and cheminformatics
representations.
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Date
2024-08-28
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Dissertation