  Recent discovery of new materials for thermoelectric energy conversion is
enabled by efficient prediction of materials' performance from
first-principles, without empirically fitted parameters. The novel simplified
approach for computing electronic transport properties is described, which
achieves good accuracy and transferability while greatly reducing complexity
and computation cost compared to the existing methods. The first-principles
calculations of the electron-phonon coupling demonstrate that the energy
dependence of the electron relaxation time varies significantly with chemical
composition and carrier concentration, suggesting that it is necessary to go
beyond the commonly used approximations to screen and optimize materials'
composition, carrier concentration, and microstructure. The new method is
verified using high accuracy computations and validated with experimental data
before applying it to screen and discover promising compositions in the space
of half-Heusler alloys. By analyzing data trends the effective electron mass is
identified as the single best general descriptor determining material's
performance. The Lorenz number is computed from first principles and the
universality of the Wiedemann-Franz law in thermoelectrics is discussed.
