Electron and Phonon Transport
Transport properties from first principles
Electronic and thermal conductivities govern the performance of many types of devices such as thermoelectrics, power electronics, photovoltaics, and sensors. Predictions of transport properties from quantum first principles are difficult because in addition to energies (spectra) of electrons and phonons, one also needs to compute their lifetimes that depend on their interactions. By combining density functional perturbation theory with Boltzmann transport formalism, we develop computational methods to predict and understand electrical and thermal transport properties of materials from first principles. We start with electronic and vibrational structure obtained from DFT. We then obtain scattering rates and transport properties using the electron-phonon calculations from Wannier interpolation as well as the within the more computationally efficient electron-phonon averaged (EPA) approximation.
Thermoelectric materials design
Electronic and thermal conductivities govern the performance of thermoelectrics, electronics, photovoltaics and many other technologies. Ab-initio predictions of electron and phonon transport and coupling are complicated by the need to capture the multiscale dynamics and scattering of elementary excitations that cannot be explicitly obtained in atomistic computations, if their mean free paths and correlation scales are long. Our approach is to find efficient scale-separation strategies that combine analytical condensed-matter physics models describing long-range response and screening with ab-initio electronic structure computations of atomic-scale parameters, such as excitation spectra and electron-phonon and phonon-phonon couplings. Electronic and thermal transport in certain regimes can be predicted remarkably well using affordable computations, enabling quantitative understanding and design of electronic materials and random alloys for thermoelectric energy conversion. Figure below summarizes the discovery process we follow, starting from developing methods for computing electronic lifetimes to thermoelectric materials screening, synthesis and device characterization.