Highly Accurate Computational Strategies for Molecular Electronic States. – (Yann Damour / LCPQ / Thèse). – 29/10/2024, 9H00

Soutenance de thèse

Yann Damour LCPQ, Salle de conférence, 3R4

Summary:
Molecules play an important role in ourlives by surrounding us and participating in a multitude of processes. Most of these processes can be studied experimentally. However, obstacles can be encountered, such as the complexity or timescale of the process of interest, the experimental conditions and their elevated cost, the presence of dangerous chemicals, and so on. Theoretical chemistry offers a solution to these problems through numerical simulations. Unfortunately, the accuracy of these simulations is limited by computational capabilities. This requires approximations to be made, which can reduce the quality of the obtained results unless managed carefully. Therefore, reliable reference values are essential for benchmarking these simulations. In this context, this thesis aims to develop highly-accurate theoretical methods for providing reference values, focusing on wave function methods such as selected configuration interaction and coupled cluster.
We explore different theoretical approaches and various kinds of molecular electronic states. We start with the ground state of medium-sized molecules described with orbital optimized selected configuration interaction (SCI), followed by the study of molecular properties of ground and excited states, also using SCI. Then, we delve into the continuum with an adaptation of SCI for electronic resonances. After that, we study the performance of approximate coupled cluster methods with a state-specific approach to compute excitation energies, before finally proposing a stochastic approach to CCSD(T), the gold standard method of quantum chemistry.