Hi all, could you suggest me references that can help me in the following calculation? I would like to see how to describe microscopically the interaction of light (or in general of an external field) with a disordered system such as glass ( I can find literature only for materials modelled with regular lattices). Could you suggest which model has to be considered for a disordered system? To be concrete: how can microscopically 'explain' the curve permittivity or permeability vs frequancy of the external field (light) for a glass? Thanks in advance!