Two-component relativistic density functional method for computing nonsingular complex linear response of molecules based on the zeroth order regular approximation

We report the implementation of a frequency-dependent two-component relativistic density functional theory method based on the zeroth order regular approximation (ZORA) for computations of complex linear response of molecules including spin-orbit coupling. The implementation is based on Slater-type atomic orbital basis functions and makes extensive use of density fitting techniques. The complex response is obtained by applying damping in the computations. The method is validated by computations of the real and imaginary part of the static and dynamic polarizability of group 12 atoms, of a number of heavy-atom diatomic molecules, of a range of two- and three-dimensional gold clusters, and of group 8 oxides and metallocenes. Simulated spectra-a plot of extinction coefficient as a function of frequency-obtained from the isotropic imaginary polarizability are compared to broadened spectra obtained from two-component ZORA excitation energies and oscillator strengths.