In the nuclear ensemble approach, the electronic spectra are simulated using molecular configurations, here called snapshots, that we sample from different points in time during an MD trajectory at a specified temperature. For absorption, ground state MD is performed, followed by calculations of vertical excitation energy (VEE) and oscillator strength for each snapshot. For emission, excited state MD is performed, with the energy gap calculations on these snapshots representing the vertical deexcitation energy (VDE). To obtain the final optical spectrum, often a Gaussian function dresses the bare vertical energies. The linear absorption and emission crosssections using the ensemble approach are then obtained as,