Density functional theory based exploration of structural, electronic, mechanical, thermodynamic, and optical...

In this study, we performed comprehensive first-principles calculations based on density functional theory to investigate the structural, electronic, mechanical, thermodynamic, and optical properties ofα-nickel sulfide (α-NiS), with a particular emphasis on its potential for CO₂adsorption. Structural optimization confirms the stability of theα-NiS phase, yielding lattice parameters,a=b=3.425Å,c=5.286Å, in good agreement with experimental data. Electronic band structure analysis reveals a semiconducting nature with a bandgap of 1.98 eV. Mechanical and thermodynamic analyses confirm the elastic and thermal stability ofα-NiS, supporting its suitability for surface reactions. Optical property calculations indicate thatα-NiS exhibits strong absorption across a broad spectral range, highlighting its potential in photonic and catalytic systems. To evaluate its gas adsorption capabilities, CO₂adsorption on both Ni- and S-terminated surfaces was investigated. The results show that CO₂binds more strongly to the Ni-terminated surface through ionic interactions, forming Ni-O bonds with a bond length of 2.36 Å and a bond angle of 95.5°, while interaction with the S-terminated surface is weaker and predominantly covalent. The calculated adsorption energies of-2.71 eV (Ni-side) and-0.98 eV (S-side) further confirm the thermodynamic favorability of CO₂adsorption on the Ni-terminated surface, suggestingα-NiS as a promising candidate for gas capture applications.