Thursday 25 September 2025
Scientists have long been fascinated by the phenomenon of singlet fission, where a single excited molecule splits into two triplet states that can be used to generate electricity or other valuable products. However, simulating this process has proven challenging due to its complex electronic structure and the need to consider multiple molecules at once.
A recent study published in The Journal of Chemical Physics presents a new approach to modeling singlet fission using a combination of tight-binding excitonic theory and density matrix renormalization group (DMRG) calculations. The research team, led by Supriyo Santra and Debashree Ghosh from the Indian Association for the Cultivation of Science and Tata Institute of Fundamental Research, respectively, has developed a method that can accurately describe the energy states of large singlet fission molecular aggregates.
The researchers began by creating a spin-resolved tight-binding excitonic model for singlet fission, which allows them to parameterize their calculations based on ab initio results from smaller molecules. They then used DMRG to simulate the behavior of larger aggregates, including pentacene crystals. The team evaluated the resulting spectra and density of states to understand how the energy levels of the system evolve as a function of distance between the molecules.
One key finding is that the energy states of the system exhibit natural band structures in some cases, which can be used to identify specific features of the singlet fission process. By analyzing the entanglement entropy of the eigenstates, the researchers were able to gain insight into the multireference character of these states, which is important for understanding how the energy levels are populated.
The new method has several advantages over previous approaches. For example, it allows for a more accurate treatment of long-range correlations in the diabatic energies, which is critical for describing the behavior of large molecular aggregates. The DMRG calculations also provide a way to systematically optimize the energy states and ensure that they are orthonormal.
The study’s results have important implications for understanding the mechanisms of singlet fission in organic molecules, such as acenes and carotenoids. By developing more accurate models of this process, researchers can better design materials and devices that take advantage of singlet fission to generate electricity or other valuable products. The work also highlights the importance of considering both short-range and long-range correlations in molecular systems, which is essential for understanding complex chemical and physical phenomena.
Cite this article: “Modeling Singlet Fission with Tight-Binding Excitonic Theory and Density Matrix Renormalization Group Calculations”, The Science Archive, 2025.
Singlet Fission, Tight-Binding Excitonic Theory, Density Matrix Renormalization Group, Molecular Aggregates, Pentacene Crystals, Band Structures, Entanglement Entropy, Multireference Character, Diabatic Energies, Organic Molecules
