Dissertation: Dynamics of excited electronic states in functional materials

  • Date:
  • Location: Zoom: https://uu-se.zoom.us/j/69930907757
  • Doctoral student: Raquel Esteban Puyuelo
  • Contact person: Raquel Esteban Puyuelo
  • Disputation

Non-equilibrium processes involving excited electron states are very common in nature. This work summarizes some of the theoretical developments available to study them in finite and extended systems. The focus lays in the class of Mixed Quantum-Classical methods that describe electrons as quantum-mechanical particles but approximate ionic motion to behave classically. In particular, Non-Adiabatic Molecular Dynamics and Real Time Density Functional Theory are described and applied to answer questions regarding non-equilibrium dynamics in diverse functional materials. First, the effect of phase boundaries and defects in monolayer MoS2 samples is studied. This material has been suggested as a good candidate to substitute silicon in many applications, such as flexible electronics and solar cells. It is known that defects and different polymorphs are present in experimental samples, and therefore it is extremely important to understand how realistic samples perform. We present how the electron-hole recombination times are accelerated in presence of defects, as well as how the structural changes in samples that mix several phases of MoS2 affect their electronic structure. After that, rectangular graphene nanoflakes are explored. As an application to finite systems, we show in rectangular graphene nanoflakes how different magnetic configurations have distinct optical absorption spectra and how this can be used for opto-electronic applications. Furthermore, the high harmonic generation for different magnetic couplings is studied, showing how some harmonics can be suppressed or enhanced depending on the underlying electronic structure. Finally, diffuse scattering in SnSe is investigated in an experimental collaboration in order to understand how phonon-phonon interactions affect the scattering dynamics, which may lead to profound insight into its thermoelectric properties.