First-principles calculations of spin-split bands in chiral hybrid organic-inorganic perovskites (R/S-PEA)PbI₃ and (R/S-NEA)PbI₃

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Chiral hybrid organic-inorganic perovskites provide a promising platform for investigating the physics of chirality-driven spin-split bands because they combine robust molecular chirality with strong spin-orbit coupling from heavy inorganic ions. First-principles calculations including spin-orbit coupling are performed for the one-dimensional chiral perovskites (R/S-PEA)PbI₃ and (R/S-NEA)PbI₃ to compare their spin-split band structures and to identify the factors controlling their differences. In (R/S-PEA)PbI₃, the lowest conduction bands predominantly consist of Pb orbitals, whereas in (R/S-NEA)PbI₃, they are formed by hybridization between Pb orbitals and the lowest unoccupied molecular orbital of NEA. Both compounds exhibit pronounced spin splitting near the valence-band maximum and conduction-band minimum. The effective spin splitting of the edges of the valence bands is stronger in (R/S-NEA)PbI₃, despite similar linear-in-k splitting coefficients near the relevant high-symmetry points. This enhancement originates from larger gaps induced by spin-orbit coupling at high-symmetry points and band (anti)crossings in the multiband structure. For a given molecular handedness, the PEA- and NEA-based compounds exhibit opposite spin textures, consistent with the opposite chiral distortions of the [PbI₆]⁴⁻ octahedra and with the previously observed opposite signs of circular dichroism. Group-theoretical analysis for the nonsymmorphic space group P2₁2₁2₁ further accounts for band sticking, symmetry-enforced degeneracies, and the disappearance of spin polarization at specific Brillouin-zone-boundary points. These results provide a solid foundation for future studies of chirality-dependent electromagnetic responses, including circular dichroism, in chiral hybrid organic-inorganic perovskites.