The Einstein solid is composed of single-frequency quantum harmonic oscillators, ϵ ϵ = ℏ ℏ ω ω = h ν ν . That frequency, if it indeed existed, would be related to the speed of sound in the solid. If one imagines the propagation of sound as a sequence of atoms hitting one another, then the frequency of oscillation must correspond to the minimum wavelength sustainable by the atomic lattice, λ λ m i n , where