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Diabatic strategies for photochemical quantum dynamics

Benjamin Lasorne, Institut Charles Gerhardt (Montpellier)

Séminaire LCPQ

Salle de séminaire IRSAMC

Jeudi 2 Octobre 2014, 14h-15h

Quantum dynamics simulations applied to ultrafast photoinduced processes often require an adiabatic-to-diabatic transformation (diabatisation) of the data produced from quantum chemistry calculations. The vibronic coupling Hamiltonian (VCH) quasidiabatic model developed by Köppel and coworkers is a fruitful strategy that has been used for calculating photoabsorption and photoelectron spectra with the multiconfiguration time-dependent Hartree (MCTDH) quantum dynamics approach. We present here a set of strategies to generalise the VCH model to the treatment of photochemical reactions whereby large-amplitude nuclear motions occur along complicated reaction pathways connecting several potential energy wells through transition barriers. This is illustrated on the photoisomerisation of ethylene [1] and the ring opening of benzopyran [2]. A global model based on local information at critical points is being developed for high-dimensional quantum dynamics simulations using the novel multilayer formulation of MCTDH termed ML-MCTDH. Alternatively, the direct dynamics variational multiconfiguration Gaussian (DD-vMCG) wavepacket method frees simulations from this preliminary step by calculating the potential energy and its derivatives on the fly [2]. The quasidiabatic Hamiltonian is currently generated from a regularisation method, and work is in progress to implement a local diabatisation procedure.

[1] J. Jornet Somoza, B. Lasorne, M. A. Robb, H.-D. Meyer, D. Lauvergnat, and F. Gatti, J. Chem. Phys. 137 (2012) 084304.

[2] L. Joubert Doriol, B. Lasorne, D. Lauvergnat, H.-D. Meyer, and F. Gatti, “A generalised vibronic-coupling Hamiltonian model for benzopyran”, J. Chem. Phys. 140 (2014) 044301.

[3] D. Mendive-Tapia, B. Lasorne, G. A. Worth, M. A. Robb, and M. J. Bearpark, J. Chem. Phys. 137 (2012) 22A548.