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TY  - THES
AU  - Schultze, Jil
TI  - Tackling multi-reference systems with quantum monte carlo methods
PB  - RWTH Aachen University
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2023-11746
SP  - 1 Online-Ressource : Illustrationen
PY  - 2023
N1  - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2024
N1  - Dissertation, RWTH Aachen University, 2023
AB  - For nearly a century, the quest to accurately describe the correlation of electrons has been pursued by scientists. However, the challenging task of recovering both dynamic and static electron correlation, which is crucial for systems dominated by multiple configurations, has been encountered. In the last few decades, researchers have developed a multitude of methods carefully tailored to capture both types of correlation. Among the techniques capable of addressing this challenge are quantum Monte Carlo methods, known for their ability to provide accuracy beyond mean-field theory. The objective of this work is to explore the effectiveness and accuracy of the multi-reference diffusion Monte Carlo (MR-DMC) approach for various systems exhibiting multi-reference character. In the first part of this work, we focus on the late transition metal compounds, utilizing initial full valence complete active space self-consistent field wave functions. Accurate bond dissociation energies are reported for a variety of transition metal dimers, demonstrating close agreement with experimental results. The optimization of molecular orbitals using variational Monte Carlo in the presence of a Jastrow correlation function is identified as a key factor contributing to this success. Additionally, spectroscopic constants are investigated by fitting a Morse potential to the recorded MR-DMC potential energy curves, resulting in a good agreement with experimental and theoretical data. In the second part, we shift our attention to selected configuration interaction approaches, with a primary emphasis on a rigorous investigation of the ground state of the carbon dimer using truncated CIPSI-Jastrow wave functions. The influence of the Jastrow factor on the redistribution of importance among the different configurations is discussed. Furthermore, accurate MR-DMC absolute energies and bond dissociation energies for the carbon dimer are presented. Lastly, a selected configuration interaction algorithm in conjunction with a Jastrow correlation function is introduced.
LB  - PUB:(DE-HGF)11
DO  - DOI:10.18154/RWTH-2023-11746
UR  - https://publications.rwth-aachen.de/record/974989
ER  -