{'fraction_non_alphanumeric': 0.04023361453601557, 'fraction_numerical': 0.036340038935756006, 'mean_word_length': 5.371900826446281, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Discovery of New Phases of Bismuth Oxyselenide Semiconductor Bi2OSe2 by Global Structure Search Approach

Bi2O2X and Bi2OX2 (X = S, Se, and Te) have shown potential for thermoelectric, optoelectronic, etc. applications. The ground‐state structures of Bi2O2X have been determined experimentally (in space group I4/mmm). However, for Bi2OX2, only Bi2OS2 has been synthesized in the experiment (in space group P4/nmm). In previous theoretical studies, the crystal structures of Bi2OSe2 and Bi2OTe2 are assumed the same as that of Bi2OS2. Whether they can be experimentally synthesized remains an open question. Here, a swarm intelligence‐based structural prediction is employed in combination with first‐principles calculations to predict the crystal structures of Bi2OSe2. Three thermodynamically stable low‐energy phases (P21/m, P4/nmm, and P21/m′) are identified. Importantly, the newly reported P21/m phase, instead of the previously assumed P4/mmm phase, has the lowest energy. The P21/m‐Bi2OSe2 shows marginal stability with respect to decomposition into binary compounds Bi2O3 and Bi2Se3. The predicted phases of Bi2OSe2 have bandgaps of 0.67–1.19 eV and comparable small electron and hole carrier effective mass (less than 0.65 m0). The different phase stability between Bi2OSe2 and Bi2OS2 are explained in terms of different Bi─S and Bi─Se covalent bonding characters. Our work provides theoretical guidance for discovering new phases of Bi2OSe2 and an in‐depth understanding of the structure‐property relationship of Bi─O─S/Se system.