Thermopower, Hall tensor, and relaxation time approximation for elemental zinc

The constant relaxation time approximation is investigated through the calculation of the thermopower, anisotropy of the conductivity, and Hall tensor of elemental zinc. It is shown that this approximation is reliable at high enough temperature (greater than or similar to 150 K). Moreover, when a magnetic field is applied to the system, the relaxation time is shown to fulfill a sum rule due to Onsager reciprocity relations. This reduces the range of possible approximations for the relaxation time in Hall tensor calculations. The way in which the basic equations of transport theory have to be used to get better numerical efficiency is also discussed.