Abstract
We employ density functional theory to explore how Al and Cu substitution influence the mechanical properties of the refractory high-entropy alloy MoNbTaW. Replacing W with Al or Cu reduces the alloy's density and alters its electronic structure in distinct ways. Projected density of states and Bader charge analyses indicate that Cu weakens metallic bonding, while Al promotes more directional, covalent-like interactions. These modifications enhance ductility, as evidenced by increases in Poisson's ratio ( v ) and the Pugh ratio ( γ ). Electron localization function results further reveal greater charge delocalization in the alloyed systems, supporting the conclusion that strategic Al and Cu incorporation can improve ductility without compromising thermodynamic stability. These findings provide insight into designing lightweight, ductile, and stable tungsten-based high-entropy alloys for demanding structural applications.