How to Construct Diabatic States for Energy and Charge Transfer with Subsystem Quantum Chemistry─A Tutorial

Making use of fragment-based quantum chemical methods provides powerful tools for studying a wide range of energy- and charge-transfer processes, owing to their intrinsic diabatization capabilities and reduced computational cost. Furthermore, we argue that, given user-friendly software, such approaches are, in principle, easier to apply than alternative mixed quantum mechanical-molecular mechanics procedures. In this tutorial, our goal is to illustrate how fragment-based quantum chemical methods can be applied to (i) energy-transfer and (ii) charge-transfer processes with relative ease, using the Python wrapper Serenipy of the fragment-based quantum chemistry program Serenity, which is now conveniently available via PyPI. To this end, we guide the reader through a series of illustrative case studies and provide additional recommendations aimed at making fragment-based quantum chemical methods more accessible to a broader community.