If we assume that the electrons behave as a classical ideal gas and obey
Maxwell–Boltzmann statistics, the heat capacity per mole is found to be 3R/2
or 3NAkB/2, where NA is Avogadro’s number. To convert this to heat capacity
per unit volume for use in Equation 12.19, we must multiply by the ratio of the
electron density to Avogadro’s number. Thus,