Understanding the emergence of electronic and magnetic properties in molecular quantum materials

• Applicant: Dr. Johannes Tölle
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation ; Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 577598009

Molecular quantum materials exhibit a wide range of magnetic and electronic properties, making them a unique platform for studying fundamental physical effects arising from strong electronic interactions. Their structural diversity and, in principle, straightforward chemical modification enable fine-tuning of these properties for large-scale applications. However, achieving this requires uncovering the microscopic mechanisms responsible for these properties. The strong electronic interactions make identifying these mechanisms particularly challenging. While experimental characterization of various properties is indispensable, it often provides only indirect insights into the underlying microscopic processes, frequently resulting in competing interpretations. In contrast, theoretical numerical simulations allow for a direct investigation of these mechanisms. Due to their complexity, molecular quantum materials have traditionally been studied using phenomenological model Hamiltonians. Despite many successes, this approach has limitations when it comes to predicting material-specific properties, ensuring systematic improvability, and error control. The objective of this programme is to develop a general, systematically improvable ab initio framework for simulating molecular quantum materials, which relies on: 1) Improvements to ab initio quantum embedding protocols; 2) The development of new, accurate, and systematically improvable diagrammatic electronic structure methods; 3) The incorporation of electron-phonon coupling; and 4) Tensor decomposition techniques for efficient numerical implementation. Within this framework, the accuracy of calculated properties can be systematically improved by a) increasing the size of the embedding region, b) including higher-order diagrammatic or coupling contributions, and c) tightening decomposition thresholds. The framework will be applied to study charge disproportionation in two-dimensional charge-transfer salts, as well as their superconducting properties. Furthermore, the role of non-adiabatic electron-phonon interactions in alkali-metal fullerides will be investigated.

• DFG Programme: Emmy Noether Independent Research Groups