To model electron transfer events and charging at the atomic scale in a non-empirical, predictive way, one must employ electronic structure theory such as density functional theory (DFT). Unfortunately, this restricts the system size to a few hundred explicit atoms, too small to account for long-range electrostatic interactions that substantially influence the charge distribution and energy landscape. Instead, the simulations employ artificial boundary conditions that must later be linked to the situations of interest. With various examples, I will summarize our general strategy to derive corrections for finite-size artifacts when modelling localized charges, and show that such corrections reduce finite-size effects significantly and in a controlled way. I will then discuss some of the prospects of mapping medium-range electrostatic effects at the DFT level to scalable models. Electronic structure theory encompasses metallic and dielectric screening in parallel. I will explain why capturing local polarisation will be the key to flexible, consistent, and transferable coarse-grained electrostatic models. Challenges lie in the non-locality of screening at the quantum level and the disentangling of short-range and long-range potential fluctuations.
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