Geometrical features, stability and hydrogen positions in (Al2Cu)n clusters

Abstract

The phase equilibria of the Al-Cu alloys have been well-established, with the Al₂Cu being a crucial component of the phase diagram. Constructing an atomic model with a 2:1 stoichiometric ratio of Al and Cu holds significance for further investigating the local structures of the alloy phases. Here, we employ the GA-DFT method to explore the structural potential energy surfaces of (Al₂Cu)_n clusters (n = 1–6). The results reveal that the (Al₂Cu)_n evolve from hollow cages to more densely packed configurations, with Al atoms relatively more concentrated and Cu atoms becoming more dispersed throughout the structures. The E_b and Δ₂E analyses show that the (Al₂Cu)₃ has a higher stability than that of its neighbors, and the AIMD simulations demonstrate that it can maintain the structural integrity at 700 K. The molecular orbitals reveal that 21 valence electrons of the (Al₂Cu)₃ fill superatomic orbits resulting in an electronic configuration of 1S²1P⁶1D¹⁰2S²1F¹, which is also confirmed by the density of states. The good stability of the (Al₂Cu)₃ allows the bonding of the H atom to it without causing significant deformation changes in the parent geometry, in which the H tends to preferentially locate at Al sites. The deformation of structures is particularly obvious when H is close to Cu atom.