Density-fitting method in symmetry-adapted perturbation theory based on Kohn-Sham description of monomers

We present a new implementation of symmetry-adapted perturbation theory of intermolecular interactions based on Kohn-Sham description of monomers. With density-fitting of molecular integrals, the scaling of the computational cost of the method is reduced from the sixth to the fifth power of the system size. Computational requirements of some operations scaling as the fifth power have also been significantly reduced. The new method allows an accurate treatment of molecules consisting of as many as a few dozen of atoms, using both nonhybrid and hybrid density functionals.