Barium silicide in the metastable trigonal phase is studied using ab initio methods. The band structure and the phonon spectrum are computed and analyzed. The electron-phonon coupling is found to have a substantial contribution coming from the A1g optical mode at Γ. The superconducting transition temperature is calculated using the Allen-Dynes formula, but is found to be an order of magnitude smaller than the experimental value; some tentative explanations for the disagreement are presented.