Accurate TDDFT Absorption Spectra of Molecules on Surfaces over Full Spectral Range

Theoretically, electronic excitations can be obtained by analysing the frequency components of the time-dependent dipole moment obtained from real-time time-dependent density functional theory (RT-TDDFT) simulations. Yet, an exact treatment of electronic excitations in large systems with TDDFT is computational prohibitive. Super-resolution techniques such as compressed sensing typically fail due to the presence of a quasi-continuum of electronic excitations. We present a new approach where we combine exact short time dynamics with approximate frequency space methods. As a prototypical test system, we use an organic dye-molecule adsorbed on a semi-conductor quantum-dot surface. We calculate the entire electronic absorption spectrum of this system and find that our approach can accurately capture narrow features and a quasi-continuum of states at the same time. We see a reduction of the required amount of data points up to a factor of 40 compared to standard Fourier analysis. By doing so, our method allows us to study electronic properties of large systems in ways that are not currently possible.