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SUMMARY:CMSP News and Views Seminar Series: Quantum chemistry methods to s
 tudy strongly correlated systems – from variational to machine learning 
 approaches and its application to multiexcitonic phenomena
DTSTART;VALUE=DATE-TIME:20260914T090000Z
DTEND;VALUE=DATE-TIME:20260914T100000Z
DTSTAMP;VALUE=DATE-TIME:20260914T085524Z
UID:indico-event-11504@ictp.it
DESCRIPTION:\n	Light refreshments will be servedat 10:30 on the Leonardo B
 uilding terrace\n	(or indoor in case of bad weather)Debashree Ghosh\n	(Sch
 ool of Chemical Sciences\, Indian Association for the Cultivation of Scien
 ce)\n \nAbstract:\n\n	Polyaromatic hydrocarbons (PAHs) such as acenes hav
 e long been studied due to its interesting optical properties and low sing
 let triplet gaps. Earlier studies1\,2 have already noticed that use of com
 plete valence active space is imperative to the understanding of its quali
 tative and quantitative properties. Since complete active space based meth
 ods cannot be applied to such large active spaces\, we have used density m
 atrix renormalization group (DMRG)3 based approaches. Further small modifi
 cation to the PAH topology shows interesting new phases of behaviour in it
 s optical gaps. We have understood the effect of these effects based on sp
 in frustration due to the presence of odd membered rings. In this talk\, I
  will discuss these observations from molecular and model Hamiltonian pers
 pectives.4   Developments based on artificial neural network based confi
 guration interaction for strongly correlated systems will also be discusse
 d.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.
 \n	Such wavefunction ansatz can be applied to the study of singlet fission
  in strongly correlated systems such as acenes and carotenoids.6\,7\n	 \n
 	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. C
 hem. Phys.\, 127(13)\, 134309 (2007). 2. Singlet triplet gaps in polyacene
 s: 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).\n	3. Orbital Optimization in the density matrix reno
 rmalization group\, with applications to polyenes and beta carotene\, D. G
 hosh\, J. Hachmann\, T. Yanai\, G. K.-L. Chan\, J. Chem. Phys.\, 128(14)\,
  144117 (2008).\n	4. In the quest for a stable triplet state in small poly
 aromatic hydrocarbons: an in silico tool for rational design and predictio
 n\, M. Rano\, S.K. Ghosh\, D. Ghosh\, Chemical Science\, 10\, 9270 (2019).
 \n	5. Configuration interaction trained by neural networks : Application t
 o model polyaromatic hydrocarbons\, S.K. Ghosh\, M. Rano\, D. Ghosh\, J. C
 hem. Phys.\, 154\, 094117 (2021).\n	6. Mechanism of singlet fission in Car
 otenoids from a Polyene Model System\, S. Santra\, J. Ray\, D. Ghosh\, J. 
 Phys. Chem. Lett.\, 13(29)\, 6800 (2022).\n	7. Excitonic Hamiltonian for s
 inglet fission: Beyond a dimer model\, S. Santra\, A. Bose\, D. Ghosh\, J.
  Chem. Theory Comput.\, 22(9)\, 4666 (2026).\n	 \n\n	Zoom registration li
 nk:https://zoom.us/meeting/register/Iz8pt9YoTcm_v5yb6UKSQQ\n	 \n\n//indic
 o.ictp.it/event/11504/
LOCATION:Euler Lecture Hall (Leonardo Building) and via Zoom
URL://indico.ictp.it/event/11504/
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