My compound under investigation are cubic and construct corresponding 2x2x2 supercell. Properties like optical and mechanical seems to be correct as expected. But problem arises in their electronic band structures where it changes from indirect band gap to direct band gap semiconductor. Is this even possible? Can any enlighten me with some literatures where such findings occur in pristine supercells?
Your problem may be caused by two factors: firstly, the lattice constants are not fully relaxed, and this induces residual strains and relaxation when you create supercells. 2ndly, the material may have internal freedom and the tendency of developing ferroelectric orders. Both factors may lead to the change of band structure. Another reason would be related to the band folding. It is possible that the indirect band structure of a primitive cell converts to a direct band structures based on supercell. You can try to create different shapes and sizes of supercells to see if any changes on the band structures to make different ways of band folding. Below are some literatures for references on electronic structures associated with strains etc:
1. Xuefei Yan, Xiangyue Cui, Bowen Wang, Hejin Yan, Yongqing Cai*, Qingqing Ke*, Surface asymmetry induced turn-overed lifetime of acoustic phonons in monolayer MoSSe. iScience, 26 (5) (2023);
2. Changmeng Huan, Yongqing Cai*, Devesh R. Kripalani, Kun Zhou, and Qingqing Ke*, Abnormal behavior of preferred formation of the cationic vacancies from the interior in a γ-GeSe monolayer with the stereo-chemical antibonding lone-pair state. Nanoscale Horiz. 8, 404-411 (2023)
3. Changmeng Huan, Pu Wang, Binghan He, Yongqing Cai*, and Qingqing Ke*, Highly modulated dual semimetal and semiconducting γ-GeSe with strain engineering. 2D Materials 9 045014 (2022)
4. Devesh R. Kripalani, Yongqing Cai*, Jun Lou, and Kun Zhou*, Strong edge stress in molecularly thin organic–inorganic hybrid Ruddlesden–Popper perovskites and modulations of their edge electronic properties. ACS Nano 16, 1, 261–270 (2022)
5. Yan Shao, Wei Gao, Hejin Yan, Runlai Li, Ibrahim Abdelwahab, Xiao Chi, Lukas Rogée, Lyuchao Zhuang, Wei Fu, Shu Ping Lau, Siu Fung Yu*, Yongqing Cai*, Kian Ping Loh*, and Kai Leng*, Unlocking surface octahedral tilt in two-dimensional Ruddlesden-Popper perovskites. Nat. Commun. 13, 138 (2022)
Thank you Yongqing Cai for your precious reply. In fact, the indirect band gap nature is preserved when 2x1x1 supercells are build. Does this suggest that this variation could be due to band folding? Or in other words can we assume that though this variation occurs, our calculations still stand correct?
I guess your calculation is still correct. In such supercell calculations, we only get band gap value from the calculation, and the direct/indirect nature is hard to tell from it. The latter needs to be read from a calculation on primitive cell.
Very much thanks to you sir Yongqing Cai for clarifying the confusion regarding such bandgap behaviour. Also can you please suggest some articles where such transition occurs due to supercells?
You can refer to this paper "Chem. Mater. 2022, 34, 1020−1029". This paper about PbI2 which is an indirect semiconductor in the monolayer. However, with constructing supercell, it looks like to have a direct gap.
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