Complex molecular systems studied by modern ab initio multireference methods

• Applicant: Professor Dr. Michael Roemelt
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: from 2018 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 394718827

• Final Report Year: 2025

Final Report Abstract

As part of this Emmy Noether project, we have developed and implemented novel multireference electronic structure methods tailored for systems with many strongly correlated electrons. Key advancements include a new active space selection tool, a spin-adapted heat-bath configuration interaction (HCI) solver, and nuclear gradient calculations for state-averaged HCISCF energies. These methods, along with established electronic structure techniques, were applied to investigate the chemical and spectroscopic properties of a diverse set of molecular systems, including monoand dinuclear transition metal complexes and organic photoswitches. Our results provide insight into these systems, laying the groundwork for systematic methodological improvements.

Publications

• Active Space Selection Based on Natural Orbital Occupation Numbers from n-Electron Valence Perturbation Theory. Journal of Chemical Theory and Computation, 15(6), 3522-3536.
  Khedkar, Abhishek & Roemelt, Michael
  
• Multireference Approaches to Spin‐State Energetics of Transition Metal Complexes Utilizing the Density Matrix Renormalization Group. Advanced Theory and Simulations, 2(5).
  Roemelt, Michael & Pantazis, Dimitrios A.
  
• An Ab Initio Computational Study of Electronic and Structural Factors in the Isomerization of Donor–Acceptor Stenhouse Adducts. The Journal of Physical Chemistry A, 124(38), 7756-7767.
  Ugandi, Mihkel & Roemelt, Michael
  
• An ab initio multireference study of reductive eliminations from organoferrates(iii) in the gas-phase: it is all about the spin state. Physical Chemistry Chemical Physics, 22(31), 17677-17686.
  Khedkar, Abhishek & Roemelt, Michael
  
• Electrochemically Catalyzed Newman–Kwart Rearrangement: Mechanism, Structure–Reactivity Relationship, and Parallels to Photoredox Catalysis. The Journal of Organic Chemistry, 85(12), 8029-8044.
  Roesel, Arend F.; Ugandi, Mihkel; Huyen, Nguyen Thi Thu; Májek, Michal; Broese, Timo; Roemelt, Michael & Francke, Robert
  
• Extending the ASS1ST Active Space Selection Scheme to Large Molecules and Excited States. Journal of Chemical Theory and Computation, 16(8), 4993-5005.
  Khedkar, Abhishek & Roemelt, Michael
  
• Insight into the X‐ray absorption spectra of Cu‐porphyrazines from electronic structure theory. International Journal of Quantum Chemistry, 121(3).
  Boydas, Esma Birsen; Winter, Bernd; Batchelor, David & Roemelt, Michael
  
• New Phosphorous-Based [FeFe]-Hydrogenase Models. Catalysts, 10(5), 522.
  Wittkamp, Florian; Boydas, Esma Birsen; Roemelt, Michael & Apfel, Ulf-Peter
  
• Modern multireference methods and their application in transition metal chemistry. Physical Chemistry Chemical Physics, 23(32), 17097-17112.
  Khedkar, Abhishek & Roemelt, Michael
  
• Organic Mixed-Valence Compounds and the Overhauser Effect in Insulating Solids. The Journal of Physical Chemistry A, 125(3), 867-874.
  Pylaeva, Svetlana; Marx, Patrick; Singh, Gurjot; Kühne, Thomas D.; Roemelt, Michael & Elgabarty, Hossam
  
• A recursive formulation of one‐electron coupling coefficients for spin‐adapted configuration interaction calculations featuring many unpaired electrons. International Journal of Quantum Chemistry, 123(5).
  Ugandi, Mihkel & Roemelt, Michael
  
• Electrochemistry and Reactivity of Chelation‐stabilized Hypervalent Bromine(III) Compounds. Chemistry – A European Journal, 28(42).
  Mohebbati, Nayereh; Sokolovs, Igors; Woite, Philipp; Lõkov, Märt; Parman, Elisabeth; Ugandi, Mihkel; Leito, Ivo; Roemelt, Michael; Suna, Edgars & Francke, Robert
  
• A configuration‐based heatbath‐CI for spin‐adapted multireference electronic structure calculations with large active spaces. Journal of Computational Chemistry, 44(31), 2374-2390.
  Ugandi, Mihkel & Roemelt, Michael
  
• Another Torture Track for Quantum Chemistry: Reinvestigation of the Benzaldehyde Amidation by Nitrogen‐Atom Transfer from Platinum(II) and Palladium(II) Metallonitrenes. Israel Journal of Chemistry, 63(7-8).
  Verplancke, Hendrik; Diefenbach, Martin; Lienert, Jonas N.; Ugandi, Mihkel; Kitsaras, Marios‐Petros; Roemelt, Michael; Stopkowicz, Stella & Holthausen, Max C.
  
• Oxygen sensitivity of [FeFe]-hydrogenase: a comparative study of active site mimics inside vs. outside the enzyme. Physical Chemistry Chemical Physics, 26(28), 19105-19116.
  Yadav, Shanika; Haas, Rieke; Boydas, Esma Birsen; Roemelt, Michael; Happe, Thomas; Apfel, Ulf-Peter & Stripp, Sven T.
  
• The trials and triumphs of modelling X-ray absorption spectra of transition metal phthalocyanines. Physical Chemistry Chemical Physics, 26(30), 20376-20387.
  Boydas, Esma Birsen & Roemelt, Michael
  
• Analytical SA-HCISCF Nuclear Gradients from Spin-Adapted Heat-Bath Configuration Interaction. Journal of Chemical Theory and Computation, 21(8), 3930-3944.
  Ugandi, Mihkel & Roemelt, Michael
  
• High-Spin Manganese(V) in an Active Center Analogue of the Oxygen-Evolving Complex. Journal of the American Chemical Society, 147(9), 7336-7344.
  Ablyasova, Olesya S.; Ugandi, Mihkel; Boydas, Esma B.; da Silva Santos, Mayara; Flach, Max; Zamudio-Bayer, Vicente; Roemelt, Michael; Lau, J. Tobias & Hirsch, Konstantin