Electronic structure of BaBiO3 and electron-phonon coupling in K-doped superconducting bismuthate-A first-principles study

The electronic structure of BaBiO3 and Ba1-xKxBiO3, where x = 0.375, 0.4, and 0.425 is investigated using the density functional theory (DFT) in the generalized gradient approximation (GGA). The charge-density-wave (CDW) nature of the host compound is suppressed via potassium doping at Ba-site, resulting in the emergence of a metallic state. A strong hybridization between Bi-6s and O-A(1g) orbitals is observed in the electronic states near the Fermi level, particularly enhanced in the collapsed BiO6 octahedra of the undoped compound. The K-doped systems show stronger sp(sigma) hybridization than that of the host compound. The self-doped holes condensate in the antibonding combination of Bi-s and O-A(1g) orbitals of both the doped systems and in the collapsed octahedra of the undoped system. The exploration of lattice dynamics and electron-phonon coupling in Ba1-xKxBiO3 systems, elucidate that mainly the phonons corresponding to the oxygen bond stretching vibrations contribute most to the total electron-phonon coupling. The GGA-calculated electron-phonon coupling constants (lambda) across varying K-concentrations inadequately account for experimental T(c)s. The inclusion of long-range interactions through the HSE06 hybrid exchange-correlation functional substantially augments both lambda and T-c, closely mirroring experimental observations and underscoring the crucial role of nonlocal correlations in these systems .