How large an effect should acoustic phonons produce? Estimate the polaron mass of electrons at zero temperature due to acoustic phonons, if the band effective mass is equal to the free electron mass, the electron–phonon deformation potential energy is D = 1 eV, the speed of sound is v = 5 × 10⁵ cm/s, the density is 5 g/cm³, and the Debye temperature is 30 meV.