ボルツマン方程式
To incorporate more complex interparticle interactions, a systematic approach is necessary. One such approach is provided by Chapman–Enskog theory, which derives explicit expressions for thermal conductivity starting from the Boltzmann equation. The Boltzmann equation, in turn, provides a statistical description of a dilute gas for "generic" interparticle interactions. For a monatomic gas, expressions for formula_1 derived in this way take the form