In a second step, we express the angular dependency of the effective charge at a distance R > R d in terms of spherical harmonics. Thus, for each multipole term of order l, the integration over the angles leads to a contribution U de,l (n R ) = U l w l (n R ) where U l is the l th order interaction energy. The weighting function, w l (n R ), describes the radius dependency of the interaction strength. The total interaction energy of the droplet with its environment is given by