Subsystem DFT can be used to treat a localized impurity in a bulk system as a separate subsystem embedded in a periodic environment. Such a strategy has been employed extensively by Carter and coworkers to treat the adsorption of molecules on metal surfaces with WFT-in-DFT type calculations (see, e.g., Refs. , utilizing the DFET strat-egy as outlined in Section 4. . Recent examples concern the electrochemical reduction of CO 2 on copper , and the electrochemical hydrogenation of CO on Cu(100) .