Suppose we have a metal and a very light particle with the energy $E \simeq \text{ eV}$ moving inside the metal. Suppose next that it, although is electrically neutral, can scatter on electrons through "virtual photons" (an example is $\pi^{0}F\tilde{F}$ coupling of neutral pion to EM field).
The electrons inside the metal are quasi-free. My question: could I describe the scattering of the particle on electrons as the usual free-free scattering for the particle's eV energy range? I.e., may I simply neglect the metal band structure and boundedness of electrons and assume them to be free when considering the scattering for this energy range?