Explore density-functional theory (DFT) for simulating quantum-chemical behavior of electrons in matter through this JuliaCon 2020 talk. Dive into the DFTK package, a Julia-based platform bridging scientific communities for electronic structure simulations. Learn about the challenges in quantum-chemical modeling, the principles of DFT, and the self-consistent field procedure. Discover how DFTK aims to balance practical performance with flexibility for mathematical development. Gain insights into high-throughput screening, a posteriori error analysis, and SCF algorithms in the context of DFT. Understand the motivations behind developing DFTK and its potential impact on materials research and electronic structure theory.