Exploring Problems in Inorganic Solid-State Systems with Wavefunction-Based Molecular Spectrroscopy Methods

• Main Author: Dittmer, A.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Rheinische Friedrich-Wilhelms-Universität 2023
• Subjects: Orca
• Online Access: http://hdl.handle.net/21.11116/0000-000F-58FF-0

The present work explores the possibilities of computational protocols that combine an electrostatic embedding approach to model inorganic crystalline solid-state systems with molecular theory methods for accurate calculation of spectroscopic properties. It highlights the potential of multistep protocols that combine methods ranging from DFT to single- and multireference wavefunction-based methods to explore and understand spectroscopic observations at the theoretical level. A generalized protocol for modeling bulk properties of inorganic solid-state systems using an electrostatic embedding approach within the ORCA program suite is presented. The protocol involves applying a quantum mechanical method to a specific quantum cluster that represents a part of a solid-state system. The quantum cluster is embedded in a point charge field that accounts for the long-range electrostatic effects of the solid-state system. This approach allows the quantum cluster to operate as if it were in the bulk of a solid-state system. In particular, a newly developed automated electrostatic embedding approach within the QM/MM framework in ORCA, called Ionic-Crystal-QM/MM, is presented. Two benchmark studies are performed to evaluate the applicability of the electrostatic embedding approach and molecular methods for the calculation of bulk properties of inorganic solid-state systems. The first study focuses on the calculation of NMR nuclear shielding constants using DFT functionals and MP2. The second study investigates the calculation of band gaps using TD-DFT with a variety of DFT functionals and bt-PNO-STEOM-CCSD. Both studies show that the electrostatic embedding approach gives robust results as long as the quantum cluster is carefully embedded in a sufficiently large and charge-optimized point charge field and the quantum cluster itself is converged with respect to the desired property. When this is the case, the molecular methods can obtain the calculated bulk properties with an accuracy comparable to that expected for the ...