The dynamics of optically-excited electrons and holes at femtosecond time scales and nanometer length scales is critical in many applications including photovoltaics, photocatalysis and photodetectors. Ultrafast experiments provide insights into the relaxation of non-equilibrium carriers at the tens and hundreds of femtoseconds time scales, but do not yet directly probe shorter times with nanometer spatial resolution. Theoretical calculations can access these scales and complement such experiments, but have so far been primarily restricted to free electron models applicable to simple metals.

We combine first principles calculations of electron-electron and electron-phonon scattering rates with Boltzmann transport simulations to predict the ultrafast dynamics and transport of carriers in real materials. In particular, we calculate the distributions of hot carriers generated by plasmon decay and their transport in metallic nanostructures which guide material selection and geometry design for plasmonic energy conversion devices. We also predict the evolution of electron distributions in ultrafast experiments on noble metal nanoparticles from the femtosecond to picosecond time scales. In all these studies, we find that details in the electronic structure and electron-phonon coupling matter significantly, especially when d bands are involved. Finally calculations for multiplasmon and nonlinear processes in the ultrafast regime from the mid-IR to visible and in different geometries will be discussed. Employing a Feynman diagram approach here has been critical to determine the relevant processes.