Molecular dielectric embedding GW for ionically bonded hybrid perovskites

Ruddelsden-Popper (RP) perovskites are a class of hybrid organic-inorganic lead halide perovskites with unique optoelectronic properties. First-principles GW and GW-BSE calculations of RP perovskites' excited state properties are expensive due to the O(N^4) scaling of the RPA dielectric screening with system size. We introduce an approximation for the dielectric screening, treating RP perovskites as charged organic molecules embedded in an anionic lead halide structure. DFT and RPA polarizability calculations for organic and inorganic sublattices are carried out separately, then the RPA polarizabilities are combined into one dielectric matrix. This method assigns formal charges to estimate total inorganic/organic charge transfer, and it is successful despite the strong ionic bonds between organic ions and lead halide layers. We validate our approximation by closely reproducing the GW quasiparticle band structures for several RP perovskites, and show applicability to GW-BSE calculations on disordered cells, as calculations for the inorganic sublattice can be reused as molecules are repositioned.