In contrast to FDE-ET/FDE-diab, which use the implicit constraints in approximate FDE calculations to construct the quasi-diabatic states, also explicit constraints have been combined in terms of a Lagrangian formalism in the work on "constrained subsystem density functional theory" (CSDFT) by Pavanello and co-workers . The coupling of different quasi-diabatic states in CSDFT is realized in a similar way as in FDE-ET. The geometry was optimized with GFN2-xTB 6.4.1 . Gauge origin invariance was ensured by employing the LG(OI) scheme . The calculations were performed with Serenity on a dual AMD EPYC 7552 48-core processor with 500 GB of main memory.