> ionization was sadly impossible in the code, as the repeated volume of supercells made any unbalanced charge effectively infinite. I came up with some ways to

> ionization was sadly impossible in the code, as the repeated volume of supercells made any unbalanced charge effectively infinite. I came up with some ways to handle this, but we lacked computer power for that. Calculations of charged periodic systems are possible through the use of Ewald summation techniques (or particle mesh Ewald/related techniques). It basically introduces a homogeneous neutralizing background charge, which is unphysical and makes it so that a the total energy of a charged particle in a box converges to the "true" result as a function of 1/volume. This is applicable to both classical and quantum simulations. There is no way to do a "true" charged periodic system, but honestly that's never what you want (because true infinite systems with net charge don't exist!). You can do better than homogeneous neutralizing background charge by introducing a neutralizing electrolyte through a continuum solvent model. Here's the implementation I'm most familiar with (https://arxiv.org/abs/1601.03346 https://arxiv.org/abs/1601.03346), but I know the fully open-source JDFTx also implements this (which has a bunch of other fancy approaches to incorporating solvation into periodic DFT calculations).