Elucidating the mechanisms for morphogenesis of the highly symmetric structures of diatom valves represents a great challenge both from experimental and theoretical points of view. Diatom biosilica exhibits a hierarchical structure formation, which starts at the atomic level and evolves into different morphological patterns with growing length and time scales. Consequently, modeling has to be performed within scale-bridging approaches. In the current research proposal, we will consider the growth mechanisms of biosilica in diatoms at three different length scales. (i) At the nanometer scale we aim to understand how mono- and poly-silicic acid interacts with biomolecules that are known to be involved in diatom silica formation. Studies at this level will be mainly based on quantum mechanical methods and atomistic molecular dynamics. (ii) At the mesoscale, the self-assembly processes of peptides/proteins and polyamines will be addressed as well as their interaction with silicic acid and silica nanoparticles, and with lipid bilayers. Main modeling tools will be coarse-grained molecular dynamics and kinetic Monte-Carlo techniques. The key input parameters required for the simulation will be provided by the investigations at the nanometer level. (iii) Thirdly, we will attempt to elucidate the structure formation of the great variety of diatom morphologies on the micrometer scale within the framework of continuum models based on reaction-diffusion equations and phase field methods, strongly relying on the results obtained at the nanometer and mesoscales. The modeling activities on all those length scales will be carried out in very close collaboration with the experimental partners within the Research Unit FOR 2038, so that theory will guide specific experiments, which in turn will provide the necessary feedback for improving the theoretical models.