Electronic states of Zintl-phase solar-cell material BaSi2

First-principles calculations of the density of states (DOS) and partial charge distributions for BaSi2 revealed that the electronic states of the valence bands of BaSi2 are mainly derived from the Si 3p states of Si4 tetrahedra formed in BaSi2, while those of the conduction bands originate from the Si 3p states of Si4 and 5d states of the Ba atom. Thus, the molecular orbital diagram of BaSi2 was constructed. The origin of the large slopes at the band edges in the DOS of BaSi2, which results in a high optical absorption coefficient for the material, was discussed.