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The structural, mechanical, electronic, and optical characteristics of Alkali chalcogenide and oxychalcogenides, i.e., A 2 O 2 B 2 Se 3 (A = Sr, Ba; B = Bi, Sb), were investigated using density functional theory (DFT). After full relaxation, the obtained structural parameters are in good agreement with the experimental parameters. Furthermore, the calculated elastic stiffness C i j shows that all of the studied compounds followed the mechanical stability criteria. Ductility for these compounds was analyzed by calculating Pugh's ratio; we classified the Sr 2 O 2 Bi 2 Se 3 , Sr 2 O 2 Sb 2 Se 3 , and Ba 2 O 2 Bi 2 Se 3 as ductile, and the Ba 2 O 2 Sb 2 Se 3 as brittle. The Debye temperature and acoustic velocity were estimated. In addition, electronic and chemical bonding properties were studied from the analysis of the band structure and density of state. The main features of the valence and conduction bands were analyzed from the partial density of states. Electronic band structures are mainly contributed to by Se- 4 p and Bi- 6 p /Sb- 5 p states. Direct band gaps are 0.90, 0.47, and 0.73 eV for Sr 2 O 2 Bi 2 Se 3 , Sr 2 O 2 Sb 2 Se 3 , and Ba 2 O 2 Sb 2 Se 3 , respectively. The Ba 2 O 2 Bi 2 Se 3 compound has an indirect band gap of 1.12 eV. Furthermore, we interpreted and quantified the optical properties, including the dielectric function, absorption coefficient, optical reflectivity, and refractive index. From the reflectivity spectra, we can state that these compounds will be useful for optical applications. [ABSTRACT FROM AUTHOR]