Permittivity and permeability can be predicted based on a substance's atomic composition, with calculations possible ab initio. The dielectric function, which varies with frequency and wavenumber, is crucial for determining both permittivity and permeability. However, predicting permeability is more complex, as it involves factors like domain size and crystal structure, not just composition. For instance, adding silicon can enhance permeability despite silicon being non-ferromagnetic. Overall, while theoretical predictions for permittivity are feasible, permeability remains more challenging to ascertain.