We combine first-principles calculations and Boltzmann transport theory to study the electrical transport properties of intermetallic compound YbAl3. To accurately predict the electronic relaxation time, we use the density functional perturbation theory and Wannier interpolation techniques which can effectively treat the electron-phonon scattering. Our calculated transport coefficients of YbAl3 are in reasonable agreement with the experimentally measured results. Strikingly, we discover that in evaluating the Seebeck coefficient of YbAl3, the scattering term has a larger contribution than the band term and should be explicitly considered in the calculations, especially for the case with localized bands near the Fermi level. Moreover, we demonstrate that by reducing the sample size to less than ~30 nm, the electronic thermal conductivity of YbAl3 can be sufficiently suppressed so that the thermoelectric figure of merit can be further enhanced.
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