Efficient calculation of coupled Kohn-Sham dynamic susceptibility functions and dispersion energies with density fitting

A new algorithm based on density fitting approximation is presented for the coupled Kohn-Sham frequency-dependent dynamic susceptibilities. The method can be used with all functionals, including the hybrid ones. The susceptibilities can then be employed in calculations of dispersion energies. The scaling of the calculations is reduced from the sixth to the fifth power of the system size. This opens new avenues for accurate calculation of dispersion interactions in systems containing a few dozen atoms.