Vanadium-Engineered Co₂NiSe₄ nanomaterial: coupled thermoelectric, piezoelectric, and electronic optimization via DFT+U for advanced energy applications

• Vanadium doping enhances Co₂NiSe₄'s electronic and magnetic performance via increased DOS and spin polarization. • DFT+ U reveals improved elastic moduli and thermal stability in V-doped Co₂NiSe₄ without compromising ductility. • A high ZT of ∼1.1 at 900 K is achieved at 5 % V doping due to optimized thermoelectric parameters. • Doping broadens optical absorption, boosts dielectric response, and enables tunable reflectivity. • Piezoelectric response significantly increases with V doping, ideal for nanoscale electromechanical systems. The multifunctional potential of quaternary chalcogenides can be dramatically expanded by targeted point-defect engineering. In this work, we employ density functional theory (DFT) with on-site Coulomb correction (GGA + U) to explore the structural, electronic, optical, thermoelectric, and piezoelectric properties of pristine and dilute vanadium-doped Co₂NiSe₄ (≤ 10 at.%). Our results reveal that V substitution in monoclinic Co₂NiSe₄ introduces a resonant V d³ impurity level, which simultaneously (i) narrows the electronic band gap from 0.52 eV to 0.30 eV, (ii) lncrease the total spin moment from 3.2 to 3.6 µB per formula unit, and (iii) triples the density of states at the Fermi level (E f ). These modifications lead to a significant enhancement in electrical conductivity and phonon-defect scattering, collectively boosting the thermoelectric figure of merit (zT) up to ≈ 1.1 at 900 K for 5 at.% V. Concurrently, the dielectric onset red-shifts into the near-infrared, and the dielectric constant and absorption spectrum broaden, enabling broadband light harvesting and potential NIR optoelectronic applications. The piezoelectric modulus e₃₃ also shows a notable 23 % increase, rising to 2.70 C/m² at 10 % V doping, indicating strong electromechanical coupling driven by lattice distortion and local symmetry breaking. Simulated X-ray absorption spectra at the Co L₂,₃ edges further reveal redshifted and broadened absorption peaks upon V doping, confirming enhanced Co–V hybridization and an increased unoccupied 3d-state density, which supports improved conductivity and optical response. These mutually reinforcing electronic, vibrational, and electromechanical enhancements position V-doped Co₂NiSe₄ as a promising multifunctional material platform for integrated heat-to-power conversion, near-infrared photodetection, and spintronic or spin-filter applications. The study highlights how targeted substitutional doping in chalcogenides can unlock simultaneous improvements across energy, sensing, and actuation domains.