Starts 14 Sep 2026 11:00
Ends 14 Sep 2026 12:00
Central European Time
CMSP News and Views Seminar Series: Quantum chemistry methods to study strongly correlated systems – from variational to machine learning approaches and its application to multiexcitonic phenomena
Euler Lecture Hall (Leonardo Building) and via Zoom
Light refreshments will be served
at 10:30 on the Leonardo Building terrace
(or indoor in case of bad weather)
Debashree Ghosh
(School of Chemical Sciences, Indian Association for the Cultivation of Science)
at 10:30 on the Leonardo Building terrace
(or indoor in case of bad weather)
Debashree Ghosh
(School of Chemical Sciences, Indian Association for the Cultivation of Science)
Abstract:
Polyaromatic hydrocarbons (PAHs) such as acenes have long been studied due to its interesting optical properties and low singlet triplet gaps. Earlier studies1,2 have already noticed that use of complete valence active space is imperative to the understanding of its qualitative and quantitative properties. Since complete active space based methods cannot be applied to such large active spaces, we have used density matrix renormalization group (DMRG)3 based approaches. Further small modification to the PAH topology shows interesting new phases of behaviour in its optical gaps. We have understood the effect of these effects based on spin frustration due to the presence of odd membered rings. In this talk, I will discuss these observations from molecular and model Hamiltonian perspectives.4 Developments based on artificial neural network based configuration interaction for strongly correlated systems will also be discussed.5 The similarities between the ANNs and the MPS wavefunctions will be leveraged for 2D systems. Some new results on restricted Boltzmann machine based approaches for quantum mechanical wavefunctions show great promise.
Such wavefunction ansatz can be applied to the study of singlet fission in strongly correlated systems such as acenes and carotenoids.6,7
1. The radical character of the acenes: A density matrix renormalization group study, J. Hachmann, J.J. Dorando, M. Aviles, G.K.-L. Chan, J. Chem. Phys., 127(13), 134309 (2007). 2. Singlet triplet gaps in polyacenes: a delicate balance between static and dynamic correlations investigated by spin flip methods, C.U. Ibeji, D. Ghosh, Phys. Chem. Chem. Phys., 17(15), 9849 (2016).
3. Orbital Optimization in the density matrix renormalization group, with applications to polyenes and beta carotene, D. Ghosh, J. Hachmann, T. Yanai, G. K.-L. Chan, J. Chem. Phys., 128(14), 144117 (2008).
4. In the quest for a stable triplet state in small polyaromatic hydrocarbons: an in silico tool for rational design and prediction, M. Rano, S.K. Ghosh, D. Ghosh, Chemical Science, 10, 9270 (2019).
5. Configuration interaction trained by neural networks : Application to model polyaromatic hydrocarbons, S.K. Ghosh, M. Rano, D. Ghosh, J. Chem. Phys., 154, 094117 (2021).
6. Mechanism of singlet fission in Carotenoids from a Polyene Model System, S. Santra, J. Ray, D. Ghosh, J. Phys. Chem. Lett., 13(29), 6800 (2022).
7. Excitonic Hamiltonian for singlet fission: Beyond a dimer model, S. Santra, A. Bose, D. Ghosh, J. Chem. Theory Comput., 22(9), 4666 (2026).
Such wavefunction ansatz can be applied to the study of singlet fission in strongly correlated systems such as acenes and carotenoids.6,7
1. The radical character of the acenes: A density matrix renormalization group study, J. Hachmann, J.J. Dorando, M. Aviles, G.K.-L. Chan, J. Chem. Phys., 127(13), 134309 (2007). 2. Singlet triplet gaps in polyacenes: a delicate balance between static and dynamic correlations investigated by spin flip methods, C.U. Ibeji, D. Ghosh, Phys. Chem. Chem. Phys., 17(15), 9849 (2016).
3. Orbital Optimization in the density matrix renormalization group, with applications to polyenes and beta carotene, D. Ghosh, J. Hachmann, T. Yanai, G. K.-L. Chan, J. Chem. Phys., 128(14), 144117 (2008).
4. In the quest for a stable triplet state in small polyaromatic hydrocarbons: an in silico tool for rational design and prediction, M. Rano, S.K. Ghosh, D. Ghosh, Chemical Science, 10, 9270 (2019).
5. Configuration interaction trained by neural networks : Application to model polyaromatic hydrocarbons, S.K. Ghosh, M. Rano, D. Ghosh, J. Chem. Phys., 154, 094117 (2021).
6. Mechanism of singlet fission in Carotenoids from a Polyene Model System, S. Santra, J. Ray, D. Ghosh, J. Phys. Chem. Lett., 13(29), 6800 (2022).
7. Excitonic Hamiltonian for singlet fission: Beyond a dimer model, S. Santra, A. Bose, D. Ghosh, J. Chem. Theory Comput., 22(9), 4666 (2026).