First-principles calculations of the electronic structure and optical properties of LiB3O5, CsB3O5, and BaB2O4 crystals

This paper reports the calculation of electronic structure and linear optical properties of LiB3O5 (LBO), CsB3O5 (CBO), and BaB2O4 (BBO) crystals using the linearized augmented plane-wave band method. It is found that the top of their valence bands consists of O orbitals, while the boron has almost no contribution. The linkage between (B3O7)(5-) anionic groups in the crystalline state is the main cause of making the gap of LBO and CBO larger than BBO's. The near-edge interband transition contains the contribution of the trigonal coordinated B-O bands in the final state for LBO. For CBO and BBO, the final state consists mainly of cation states at the bottom of the conduction bands. In this case, however, the transition from the O derived valence states to these cation states is quite weak; strong transition only appears till about 1 eV above the absorption edge when B-O orbitals are also involved in the final states.