As mentioned in the RT-TDDFTB theory and methodology section, a groundstate DFTB+ calculation for naphthalene must be carried out first before performing an RT-TDDFTB calculation. With the ground-state DFTB+ calculation for naphthalene properly converged, one obtains the non-self-consistent Hamiltonian matrix, the self-consistent Hamiltonian matrix, the initial single-electron density matrix, and the overlap matrix as output files. Next, to compute an absorption spectrum of naphthalene, 3 independent simulations must be carried out in which the system is excited with a very short electric pulse (i.e., a Dirac delta pulse) that is applied in 3 mutually orthogonal directions to compute the polarizability tensor. Once the RT-TDDFTB electron dynamics calculation finishes, the time-dependent dipole moment is obtained, as shown in Fig. . Figure : Time-dependent dipole moment for a naphthalene molecule obtained by applying a Dirac delta electric field pulse to the system.