title: Quantum-classical effective-modes dynamics of the pipi* --> npi* decay in 9H-adenine. A quadratic vibronic coupling model.
abstract: We present mixed quantum-classical simulation of the internal conversion between the lowest energy pipi* (S(La)) and npi* (S(n)) excited electronic states in adenine in the gas phase, adopting a quadratic vibronic model (QVC), parametrized with the help of PBE0 density functional calculations. Our approach is based on a hierarchical representation of the QVC Hamiltonian and a subsequent treatment of the most relevant coordinates at accurate time-dependent quantum level and of the other 'bath' modes at classical level. We predict an ultrafast transfer (-30 fs) of approximately 75% of the initial population excited on S(La) to S(n). Within an adiabatic picture, on the same timescale the wave packet concentrates almost completely on the lowest S1 state, where however it shows a very broad distribution with different characteristics (due to the different 'diabatic' character). It is shown that the proposed methodology offers a practicable route to describe the quantum dynamics of internal conversion processes in large semi-rigid systems.
authors.affiliation: Scuola Normale Superiore di Pisa, Piazza dei Cavalieri 7, I-56126 Pisa, Italy.
authors.forename: David
authors.initials: D
authors.lastname: Picconi
authors.forename: Francisco José Avila
authors.initials: FJ
authors.lastname: Ferrer
authors.forename: Roberto
authors.initials: R
authors.lastname: Improta
authors.forename: Alessandro
authors.initials: A
authors.lastname: Lami
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Santoro
mesh_terms: D000225:Adenine / Q000737:chemistry*; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation
chemical_list: D000225:Adenine