First-principles and cluster expansion investigation of Ti-V-Mn AB₂ alloys: stability, electronic structure, and...

Ti-V-Mn AB₂-type alloys are promising materials for hydrogen storage applications, but their intrinsic properties are strongly influenced by chemical composition and atomic ordering. The large number of possible atomic configurations makes it challenging to establish how configurational ordering governs the energetic, electronic, and mechanical behaviour of these alloys. In this study, a combined cluster expansion and first-principles approach is used to investigate the relationship between atomic configuration and the energetic, electronic, and mechanical properties of selected ground-state Ti-V-Mn AB₂ configurations. Among the three selected configurations, Ti₈V₉Mn₇ exhibits the most negative heat of formation, indicating the most favourable formation energetics within the investigated structures. All configurations exhibit metallic character, with states near the Fermi level predominantly derived from Ti, V, and Mn 3d orbitals. The calculated elastic properties indicate mechanical stability for all three structures, while Ti₈V₈Mn₈ exhibits the highest bulk, shear, and Young's moduli. Ti₄V₆Mn₂ has the highest calculated Pugh ratio and Poisson's ratio, indicating the greatest predicted ductility among the investigated configurations. These results demonstrate that configurational ordering influences the energetic, electronic, and elastic properties of Ti-V-Mn alloys and provide a computational baseline for subsequent investigations of hydrogen-related behaviour.

Cluster expansion calculations were performed using the UNCLE code within the MedeA computational environment to explore configurational energetics and construct the ground-state convex hull. Selected ground-state configurations were subsequently investigated using spin-polarised density functional theory as implemented in the Vienna Ab initio Simulation Package (VASP), employing the GGA-PBE exchange-correlation functional and projector augmented-wave potentials with a plane-wave basis. Structural optimisation, partial and total densities of states, and elastic constants were calculated. Brillouin zone sampling used a gamma-centred k-point mesh with a k-spacing of 0.5 Å⁻¹, while first-order Methfessel-Paxton smearing with a width of 0.2 eV was applied. Bulk, shear, and Young's moduli were obtained using the Voigt-Reuss-Hill approximation, and Pugh ratios and Poisson's ratios were used to assess the predicted ductile or brittle behaviour.