where ω i and µ i are the frequency and the reduced mass of the i th vibrational mode. For the purpose of excited state dynamics simulations following an impulsive photoexcitation, and within the Franck-Condon approximation, nuclear modes are assumed to be in thermal equilibrium on the electronic ground state for which {ω i } and {µ i } are calculated. Likewise, the initial electronic state population is assumed to be 1 in the initial photo-excited state i and zero for all other states,