µ µ µ ge , µ µ µ ge(τ) and µ µ µ e(τ) f are the matrix elements of the TDMs operators between the corresponding electronic states, while U eg (R g (τ)), U e(τ)g (R e (τ)) and U f e(τ) (R e (τ)) are the transition frequencies (or, equivalently, energy gaps) between the corresponding electronic states. The notion e(τ) means that a trajectory initiated in an excited state e may jump into another electronic state.