First-principles computational techniques enable studies of materials with unprecedented accuracy. In particular, many-body perturbation theory is capable of predicting electronic and optical properties in excellent agreement with experiment. Real-time time-dependent density functional theory is an accurate yet efficient approach to describe real-time electron dynamics through time-dependent quantum-mechanical theory.<br/>This talk will first illustrate how this can be used to establish structure-property relationships between crystal phase and optical spectra. We compare wurtzite-ZnO to the non-equilibrium BN phase of ZnO that has been reported for thin films and nanostructures. Based on detailed studies of electronic properties and optical anisotropy, we show that it is possible to reliably distinguish these two phases optically. From the solution of Maxwell's equations for thin films composed of both polymorphs we conclude the possibility of tuning optical properties of samples in experiment.<br/>Next, we will discuss how energetic particle radiation that can be used to change the properties of two-dimensional materials, interacts with the electronic system of the target. We apply real-time time-dependent density functional theory and Ehrenfest molecular dynamics to study a monolayer of graphene. More specifically, we compute secondary electron yield, charge transfer, energy transfer, and equilibration time-scales after impact of charged-ion projectiles. Insights from our simulations impact scientific questions related to materials design of radiation-damage-resistant materials, helium microscopy, and focused-ion beam sample manipulation and characterization.<br/>Finally, since these accurate first-principles techniques come at a high computational cost, materials databases garner significant interest in order to accelerate materials design and to facilitate reproducibility. Here we will outline how databases can help in designing heterojunctions, e.g. to find optimal electron- and hole-transport layers for new active-component materials. While this is difficult due to the limited number of materials for which band alignment is known or can easily be computed, we will show several examples to illustrate that band alignment based on branch-point energies is a good and efficient approximation that can be obtained exclusively using data from existing electronic-structure databases.

First-principles simulations of excited electronic states: Optical properties, particle radiation, and heterojunctions

2019 Spring National Meeting

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