is the Heaviside function centered at the absorption energy ha. It ensures that emission always occurs with energy gaps smaller than the excitation energy. E0J is the energy gap, and f0J is the oscillator strength, and both are calculated between SJ and S0. They are computed for each of the ( ) J p N geometries in the nuclear ensemble for state SJ. The sum runs over all these geometries, too. gLorentz is the normalized Lorentzian line shape