Description du sujet de thèse

Ultrafast photochemical and photophysical processes triggered by UV-visible light absorption involve energy, charge, matter, and information transfer. Radiationless processes, in particular, are driven by nonadiabatic couplings (NACs) between electronic states, influenced by molecular vibrations. This interaction goes beyond the Born-Oppenheimer approximation, with the adiabatic representation of the electronic problem (eigensolutions of the electronic Hamiltonian) commonly used in quantum chemistry. Especially, when two adiabatic states degenerate at a conical intersection, NACs become divergent, making the problem mathematically unstable. To address this, a global geometry-dependent unitary basis change, called the adiabatic-to-diabatic transformation (ADT), is applied to create a stable electronic basis, though this transformation is not always unique or strictly valid. Preliminary results indicate that such a transformation can be successfully achieved by the so-called state-averaged orbital-optimized variational quantum eigensolver (SA-OO-VQE) [1], an hybrid quantum/classical algorithm ("quantum" and "classical" denoting quantum and classical computers here) designed to treat ground and excited states on an equal footing, essential to describe conical intersections or avoided crossings [1,2]. The PhD student will get familiar to the method and generalize it (theory and code) to three or more states. She.he will also explore the transformation-free, ab initio diabatization method that requires no post-processing ADT on both classical and quantum computers.

[1] S. Illésová, M. Beseda, S. Yalouz, B. Lasorne, B. Senjean. Transformation-free generation of a quasi-diabatic representation from the state-average orbital-optimized variational quantum eigensolver. J. Chem. Theory Comput. 2025, 21, 11, 5457 (2025)
[2] S. Yalouz, B. Senjean, J. Günther, F. Buda, T.E. O'Brien, L. Visscher, A state-averaged orbital-optimized hybrid quantum–classical algorithm for a democratic description of ground and excited states, Quantum Sci. Technol. 6, 024004 (2021)
[3] S. Yalouz, E. Koridon, B. Senjean, B. Lasorne, F. Buda, L. Visscher, Analytical Nonadiabatic Couplings and Gradients within the State-Averaged Orbital-Optimized Variational Quantum Eigensolver, J. Chem. Theory Comput. 18, 2, 776 (2022)

Contexte de travail

Host laboratory: Department 5 "Theoretical Physical Chemistry and Modeling" at the Charles Gerhardt Institute of Montpellier, 1919 route de Mende, 34293 Montpellier.

The PhD student will work in a team including other PhD and Master's students, as well as postdoctoral fellows working on complementary topics.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.