First-principles study on the electronic properties of BaCu2S2

Using the pseudopotential plane-wave method under the density functional theory (DFT), the electronic properties of BaCu2S2 in α and β phases are calculated. The result shows that the bottom conduction band is mainly made of Ba 5d state, while the upper valence band is formed by S 3p and Cu 4d states, but both of them for β-BaCu2S2 are wider than those for α-BaCu2S2. The electron and hole effective masses for BaCu2S2 are also analyzed in detail. It is found that β-BaCu2S2 has very small hole effective masses, which implies that β-BaCu2S2 may possess a high hole mobility. Moreover, its hole effective masses are extremely anisotropic along ab plane and c axis. These properties are helpful to enhance its Seebeck coefficient, and means that β-BaCu2S2 could be a good candidate of thermoelectric materials.