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Some ABX3 perovskites exhibit different local environments (DLE) for the sameB atoms in the lattice, an effect referred to as disproportionation,distinguishing such compounds from perovskites that have single localenvironments (SLE). The basic phenomenology of disproportionation involves theabsence of B-atom charge ordering, the creation of different B-X bond lengthfor different local environments, the appearance of metal (in SLE) to insulator(in DLE) transition, and the formation of ligand holes. We point out that thisphenomenology is common to a broad range of chemical bonding patterns in ABX3compounds, either with s-p electron B-metal cations (BaBiO3, CsTlF3), or noblemetal cation (CsAuCl3), as well as d-electron cations (SmNiO3, CaFeO3). We showthat underlying much of this phenomenology is the self-regulating response,whereby in strongly bonded metal-ligand systems with high lying ligandorbitals, the system protects itself from creating highly charged cations bytransferring ligand electrons to the metal, thus preserving a nearly constantmetal charge in DLE, while creating B-ligand bond alternation and ligand-likeconduction band (ligand hole). We are asking what are the minimal theoryingredients needed to explain the main features of this SLE-to-DLEphenomenology, such as its energetic driving force, bond length changes,possible modifications in charge density and density of state changes. Using asa guide the lowering of the total energy in DLE relative to SLE, we show thatdensity functional calculations describe this phenomenology across the wholechemical bonding range without resort to special strong correlation effects,beyond what DFT naturally contains. In particular, lower total energyconfigurations (DLE) naturally develop bond alternation, gaping of the metallicSLE state, and absence of charge ordering with ligand hole formation.

Bond disproportionation, charge self-regulation and ligand holes in s-p and in d electron ABX3 perovskites by density functional theory