Relation between the Mori-Green-Kubo formulae and their Boltzmann approximation for electronic transport coefficients
The generalized Langevin equation of motion for dynamic variables is used in order to derive general expressions for electronic transport coefficients in the vicinity of a critical point. All kinetic coefficients are treated on an equal footing, in the absence of an applied magnetic field. The derivation is model independent, although cubic symmetry is assumed. Such expressions are related to the more usual Boltzmann expressions by introducing a matrix of relaxation times. The Seebeck coefficient or thermoelectric power is given some special emphasis because it cannot be defined in terms of a single relaxation time. The Mott formula is however recovered in terms of a general kernel.