where q L mn is the multipole moment of the local basis product g m (r)g n (r). Soft contributions can analogously to Eq. ( ) be computed using FFT, while remaining terms are evaluated, in contrast to Eq. ( ), analytically using spherical harmonics. The current formulation is restricted to choosing one screening charge n 0 , not discriminating between hard n 0 and soft ñ0 variants, since the gain in computational cost provided by the latter variant is negligibly small.