Nonlocality and optics of inhomogeneous systems

Nonlocal interactions play a prominent role in the optics of inhomogeneous systems. Classical discrete dipole descriptions take into account only electro-magnetic nonlocality. This is insufficient to describe correctly the inhomogeneous optical response (e.g., reflectance anisotropy) for covalently bonded systems like semiconductor surfaces. For those systems also a prominent quantum mechanical nonlocality exists. In a cellular description this can be understood easily from the behavior of the wave function. For strongly bonded systems the wave function extends across cell boundaries and when cells are polarized, neighboring cells get polarized as well. This quantum induction introduces nonlocal polarizabilities in the description. The technical details how discrete dipole models have to be adapted to use nonlocal polarizabilities in finite systems and crystalline slabs and surfaces are given in this paper. The modified method is called discrete cellular method.