Competing s‐p and p‐p Fluctuations in Charge‐Disproportionation of BaBiO₃

Here, the mechanism of charge‐disproportionation (CD) in BaBiO 3 (BBO) using density functional theory under different crystal symmetries and by employing strain as an external perturbation is investigated. The competition between Bi 6sp–O 2p (s‐p) and O 2p–O 2p (p‐p) or Bi 6p–O 2p charge fluctuations decides the electronic ground state, CD, and bond‐disproportionation (BD) in BBO. An extended Hubbard Hamiltonian involving onsite (U) and long‐range (V) coulomb repulsion is also employed to ascertain the microscopic conditions for forming the lone pair on the bismuth site. A strong tensile strain increases p‐p fluctuation and drives the system into a strong negative‐CT character, while a strong compressive strain favors s‐p fluctuation leading to the enhanced positive‐CT character. This indicates that the change transfer energy of the bulk BBO can be tuned with external strain.