Structural, Optoelectronic, Thermoelectric, and Mechanical Properties of Orthorhombic RbAgX (X = S, Se, Te) Chalcogenides: A First‐Principles Study

We investigate the structural, electronic, optical, thermoelectric, and mechanical properties of orthorhombic RbAgX (X = S, Se, Te) using density functional theory combined with Boltzmann transport calculations. All compounds are mechanically stable in the Cmcm phase. The electronic structure exhibits direct band gaps at the Γ-point, decreasing from 3.22 eV (RbAgS) to 2.09 eV (RbAgTe), reflecting enhanced Ag-X orbital delocalization along the S → Se → Te sequence. Optical spectra show strong absorption in the visible-ultraviolet region and an increase in static dielectric constant from 3.19 to 4.20. Thermoelectric calculations indicate dominant p-type transport, with RbAgSe showing the highest Seebeck coefficient, while RbAgTe exhibits reduced thermal conductivity associated with stronger phonon scattering. Analysis of charge redistribution and bonding reveals that increased Ag-X hybridization governs band-gap narrowing, carrier effective mass, and thermal transport across the series. These results establish a consistent structure-property relationship in RbAgX compounds relevant to optoelectronic and thermoelectric applications.