LAUSR

The nonadiabatic quantum dynamics (QD) of cytosine and 1-methyl-cytosine in gas phase is simualted for 250 fs after a photoexcitation to oneof the first two bright states is simulated. The nuclear wavepacket is propa-gated on the coupled diabatic potential energy surfaces of the lowest sevenexcited states, including ππ∗,nπ∗ and Rydberg states along all the vibrational degrees of freedom. We focus in particular on the interplay betweenthe bright and the dark nπ∗ states, not considering the decay to the ground electronic state. To run these simulations we implemented an automatic general procedure to parametrize linear vibronic coupling (LVC) modelswith time-dependent density functional theory (DFT) computations, and interfaced it with Gaussian package. The wavepacket was propagated with the multilayer version of the multiconfigurational time dependent Hartree method. Two different density functionals, PBE0 and CAM-B3LYP, which provides a different description of the relative stability of the lowest energydark states, were used to parametrize the LVC Hamiltonian. Part of the photoexcited population on lowest HOMO-LUMO transition (πHπ∗L) decays within less than 100 fs to a nπ∗ state which mainly involve a promotion of an electron from the Oxygen lone pair to the LUMO (nOπ∗L). The population of the second ππ∗ state decays almost completely, in<100 fs, not only to πHπ∗L and to nOπ∗L states, but also to another nπ∗L state involving the nitrogen lone pair. The efficiency of the adopted protocol allowed usto check the accuracy of the predictions by repeating the QD simulations with different LVC Hamiltonians parametrized either at the ground state minimum or at stationary structures of different relevant excited states.