Universität zu Köln

Lekat, Simon (2025). Implementation of the CAHF/CASCI Method and Application on Actinide-DOTA Complexes. PhD thesis, Universität zu Köln.

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Abstract

This thesis presents the implementation of the Configuration-Averaged Hartree-Fock (CAHF) method combined with Complete Active Space Configuration Interaction (CASCI) within the Quantum Object Library (QOL), and their application to Ac-DOTA complexes (DOTA^4- = 1,4,7,10-Tetraazacyclododecane-N,N',N'',N'''-tetraacetate). The CAHF/CASCI approach offers a computationally efficient route for accurately describing near-degenerate f-orbitals and the resulting states in lanthanide and actinide complexes. The QOL framework was extended to enable medium- and large-scale computations through a more memory-efficient integral transformation procedure. Its capabilities were further improved by introducing a unified input system, enhancing existing methods, and adding new features such as a general overlap calculation between any wave functions, a robust CASCI implementation, and the incorporation of pseudopotential (PP) spin-orbit integrals. The second part applies the CAHF/CASCI method to investigate An-DOTA complexes (for An = Pa, U, Np), focusing on ground state character, conformer stability, and ligand field splitting. Using small-core pseudopotentials (SPPs) and high-quality basis sets, a systematic trend favoring the square antiprismatic (SAP) conformer was observed, consistent with experimental findings. This study highlights the utility of the CAHF/CASCI method for exploring the electronic structure of f-element complexes and provides insights into the chemistry of actinide-DOTA systems.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Lekat, Simon simon-lekat@posteo.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-783876
Date:	2025
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Chemistry > Institute of Theoretical Chemistry
Subjects:	Chemistry and allied sciences
Uncontrolled Keywords:	Keywords Language QOL,CAHF,CASCI-SO,DOTA,actinide-complexes UNSPECIFIED
Date of oral exam:	24 April 2025
Referee:	Name Academic Title Dolg, Michael Prof. Dr. Wickleder, Mathias Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/78387