  We use our recently proposed microscopic modeling in the framework of linear
response theory to investigate the complete phonon dispersion, the phonon
density of states, certain phonon-induced electronic charge distributions and
charge fluctuations (CF's) for anomalous soft modes of metallic BaBiO$_{3}$ in
its simple cubic phase where superconductivity with $T_{c}$ up to 32 K appears.
The theoretical approach already has been applied successfully to the cuprate
high-temperature superconductors (HTSC's), simple ionic crystals (NaCl, MgO)
and perovskite oxides (SrTiO$_{3}$, BaTiO$_{3}$). It is well suited for
materials with a strong component of ionic binding and especially for "ionic"
metals. In particular, the giant phonon anomalies related to the breathing
vibration of the oxygen as found experimentally in superconducting doped
Ba$_{0.6}$K$_{0.4}$BiO$_{3}$, resembling those observed in the high $T_{c}$
cuprates, are investigated. The origin of these anomalies is explored and
attributed to a strong nonlocal coupling of the displaced oxygen ions to CF's
of ionic type, essentially of the Bi6s- and Bi6p orbital. This points to the
importance of both of these states at the Fermi energy. Starting from an
ab-initio rigid ion model (RIM) we calculate the effect on the lattice dynamics
and charge response of the most important electronic polarization processes in
the material, i.e. CF's and dipole fluctuations (DF's). Taking into account
these electronic degrees of freedom in linear response theory, we obtain a good
agreement with the measured phonon dispersion and in particular with the strong
phonon anomalies.

Superconductivity;Materials Science