Electronic structure, photoemission, inverse photoemission, and x-ray emission spectra of superconducting ${\mathrm{Ba}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{K}}_{\mathrm{x}}$${\mathrm{BiO}}_3$

The electronic structure of ${\mathrm{BaBiO}}_3$ is calculated by using the full-potential linearized augmented-plane-wave method in the local-density approximation, and the alloying effect of K additions is considered using the simple rigid-band model. The electron-phonon mechanism for the superconductivity is discussed within the rigid muffin-tin approximation. In this context, the difference of the electronic structure from the cuprate high-$T_c$ materials is elucidated in detail. Photoemission, inverse photoemission, and x-ray emission spectra are compared with experiment to check the validity of the single-particle picture for these excitations.