In a semiconductor with an arbitrary density of states, i.e. a relation of the form p = p ( φ φ ) between the density of holes or electrons p and the corresponding quasi Fermi level (or electrochemical potential) φ φ , the Einstein relation is D = μ μ q p q d p d φ φ , where μ μ q is the electrical mobility (see § Proof of the general case for a proof of this relation). An example assuming a parabolic dispersion relation for the density of states and the Maxwell–Boltzmann statistics, which is often used to describe inorganic semiconductor materials, one can compute (see density of states): p ( φ φ ) = N 0 e q φ φ k B T , where N 0 is the total density of available energy states, which gives the simplified relation: D = μ μ q k B T q .