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Contacts:
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Supervisor(s):
Prof. Filippo Lipparini and Prof. Jürgen Gauß

Title of the PhD project:
Towards the application of ab initio electronic structure methods to larger systems.

Abstract of the PhD project:
The study of molecular systems is often characterized by a subtle interplay of complex effects which require the application of expensive, yet powerful, electronic structure methods.
Specifically, the treatment of dynamic and static correlation is required to get an accurate and realistic quantum picture of such systems.
Dynamic correlation can be accurately treated using post-HF methods like Coupled-Cluster (CC). On the contrary, static correlation requires a multiconfiguration approach, that can be accounted for by the Complete Active Space Self-Consistent Field (CASSCF) method, at least as a starting point.
However, both the CC and CASSCF methods are hard to apply to medium/large systems because of their steep computational cost.
The aim of this research project is to formulate and implement an efficient computational realization of both such methods and to extend the implementation to the calculation of molecular properties. Numerical techniques, like the Cholesky decomposition of the two-electron repulsion integral matrix, will be exploited with the intention of reducing computational cost.
The new codes will then be tested on chemical systems that are involved in photophysical processes.

Publications:
• T. Nottoli, S. Burger, S. Stopkowicz, J. Gauss, and F. Lipparini; Computation of NMR shieldings at the CASSCF level using gauge-including atomic orbitals and Cholesky decomposition, J. Chem. Phys. 157, 084122-1-10 (2022)
• J. Gauss, S. Blaschke, S. Burger, T. Nottoli, F. Lipparini and S. Stopkowicz; Cholesky decomposition of two-electron integrals in quantum-chemical calculations with perturbative or finite magnetic fields using gauge-including atomic orbitals, Mol. Phys. 120, e2101562-1-10 (2022)
• T. Nottoli, J. Gauss, and F. Lipparini; Second-Order CASSCF Algorithm with the Cholesky Decomposition of the Two-Electron Integrals, J. Chem. Theor. Comp. 17, 6819-6831 (2021)
• T. Nottoli, J. Gauss, F. Lipparini; A black-box, general purpose quadratic self-consistent field code with and without Cholesky decomposition of the two-electron integrals, Mol. Phys. 119, e1974590-1-13 (2021)
• T. Nottoli, F. Lipparini; Is There a Quadruple Fe-C Bond in FeC(CO)3?, Computation 9, 95 (2021)

Oral communications at conferences:
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Poster communications at conferences:
• T. Nottoli, S. Burger, S. Stopkowicz, J. Gauss, and F. Lipparini; Computation of NMR Shieldings at the CASSCF Level Using Gauge-Including Atomic Orbitals and Cholesky Decomposition; CFF 2022 – Chemistry for the Future International Conference; Università di Pisa; Dipartimento di Chimica e Chimica Industriale, Via Giuseppe Moruzzi, 13 – Pisa, June 29 – July 1, 2022
• T. Nottoli, J. Gauss, F. Lipparini; A second-order CASSCF algorithm with the Cholesky Decomposition of the two-electron integrals; CFF 2021 – Chemistry for the Future International Conference; Università di Pisa; Dipartimento di Chimica e Chimica Industriale, Via Giuseppe Moruzzi, 13 – Pisa, June 30 – July 2, 2021
• T. Nottoli, F. Lipparini; CASSCF second-order algorithm with Cholesky Decomposition of the two-electron integrals matrix; Virtual Symposium on Chemical Theory and Computation (VS-CTC) 2020; Società Chimica Italiana; December 21 2020

Other achievements:
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