Generation of ground‐state structures and electronic properties of ternary Al_xTi_yNi_z clusters (x + y + z = 6) with a two‐stage density functional theory global search approach

Abstract

The structural and electronic properties of ternary Al x Ti y Ni z clusters, where x, y, and z are integers and x + y + z = 6, are investigated. Both Slater, Vosko, Wilks, and Nusair and B3LYP exchange-correlation (XC) functionals are employed in a two-stage density functional theory (DFT) calculations to generate these clusters. In the first stage, a minimum energy cluster structure is generated by an unbiased global search algorithm coupled with a DFT code using a light XC functional and small basis sets. In the second stage, the obtained cluster structure is further optimized by another round of global minimization search coupled with a DFT calculator using a heavier XC functional and more costly basis set. Electronic properties of the structures are illustrated in the form of a ternary diagram. Our DFT calculations find that the thermodynamic stability of the clusters increases with the increment in the number of constituent nickel atoms. These results provide a new insight to the structure, stability, chemical order, and electronic properties for the ternary alloy nanoclusters. K E Y W O R D SAl-Ti-Ni ternary alloy clusters, electronic structures, first-principles calculations, ground-state structures 1 | INTRODUCTION Atomic clusters are aggregates of atoms ranging from a few to thousands of atoms or molecules. Nanoclusters are atomic clusters with a diameter in the order of nanometers. They exhibit distinctly different electronic and structural behaviors compared with their larger size counterpart due to low dimensional and quantum confinement effects. [1] From the year 2000 onward, transition metal clusters had been intensively studied, both experimentally [2][3][4][5][6][7] and computationally. Nanoclusters, mainly binaries or ternaries, have attracted much attention due to their broad applications in catalysis, [32][33][34] magnetic-recording materials, [35] and biological applications, to name a few. For example, FeAlAu n (n = 1 − 6), [36] Fe-Co-Ni, [1,37,38] Fe-Co-Pd, [39] and Ag-Au-Pd [40] trimetallic clusters have been studied for their magnetic, electronic, and structural properties.In the search of the ground-state structures of ternary alloy clusters, one common practice is to generate them based on classical and semiclassical methods such as adoption of Gupta potential, Sutton-Chen potential, and others empirical potentials. These empirical or semiempirical results commonly show that the ground-state structures of the small clusters are in the shape of an icosahedron, whereas truncated octahedron and a truncated decahedral structure is favored by the large clusters. [2] Structural evolution of cluster can be explained and tackled by classical and semiclassical approaches, but these methods may fail if the electronic effects from valence electrons of the atoms have to be taken into account. [1,37,38] Using classical and semiclassical approaches in the search of ground-state configurations for transition metal clusters will produce unreliable results, due to the existence of localized d orbitals. ...