Bismuth sulfide ( Bi 2S3) exhibits excellent photocatalytic activity under visible light. We perform first-principles, density-function theory (DFT) calculations of the electronic structure for the Bi 2S3 with native vacancy to facilitate its applications by gaining insight into the role of native defects. We find that the Bi vacancies are effective p-type defects for Bi 2S3, while the S vacancies induce an intermediate level appearing in the band gap. Besides one Bi vacancy, the native vacancy defect at other four inequivalent positions in Bi 2S3 leads to a reduction of band gap. Moreover, the change of band gap depends on the position of native vacancy defect. The results indicate that the native defects are the most likely physical cause for the scattered band gaps obtained by experiments. The influence of native vacancy defects on the photocatalytic properties of Bi 2S3 is also discussed.
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