  Van der Waals forces as interactions between neutral and polarisable
particles act at small distances between two objects. Their theoretical origin
lies in the electromagnetic interaction between induced dipole moments caused
by the vacuum fluctuations of the ground-state electromagnetic field. The
resulting theory well describes the experimental situation in the limit of the
point dipole assumption. At smaller distances, where the finite size of the
particles has to be taken into account, this description fails and has to be
corrected by higher orders of the multipole expansion, such as quadrupole
moments and so on. With respect to the complexity of the spatial properties of
the particles this task requires a considerable effort. In order to describe
the van der Waals interaction between such particles, we apply the established
method of a spatially spread out polarisability distribution to approximate the
higher orders of the multipole expansion. We hence construct an effective
theory for effects from anisotropy and finite size on the van der Waals
potential.
