Density functional theory (DFT) simulations are performed to explore the physical features of Dy2MgS4 and Er2MgS4. Local density approximation with Hubbard potential (LDA + U) functional is utilized to examine the magnetic and electronic features. Half metallic ferromagnetic (HMF) behavior is confirmed by the spin‐resolved density of states (DOS) and band structure (BS) plots. Spin‐resolved BS and DOS show that Dy2MgS4 and Er2MgS4 for spin‐down are metallic, whereas both compounds in spin‐up show semiconductor nature with the bandgaps of 1.731 and 3.081 eV for Dy2MgS4 and Er2MgS4, correspondingly. Both compounds also feature exchange energies and crystal field splitting, indicating the magnetic characteristics. The estimated magnetic moments of X2MgS4 (X = Dy, Er) are 20μB and 12μB, correspondingly, also revealed by spin‐polarized magnetic density. Optical properties such as refractive index n(ω), absorption coefficient α(ω), dielectric constant , reflectivity R(, extinction coefficient k(ω), and optical conductivity σ(ω) are also explored. The optical bandgaps for MgX2S4 (X = Dy, Er) are 1.70 and 1.51 eV, respectively; it shows that both are transparent to visible light. Results indicate that both materials can be suitable for spintronic and solar‐cell usage.

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