Theoretical study of the structural and energetic properties of platinum clusters with up to 60 atoms

Abstract

Applying a theoretical approach that combines an efficient and fast global optimization based on genetic algorithms (GA) to search in structure space and the parameterized density-functional tight-binding (DFTB) method for the calculation of the energy for a given structure, the structures of neutral and isolated Ptn clusters are determined with size n from 4 up to 60 atoms. For the analysis of the structural, energetic, and electronic properties of Ptn as a function of n, a series of descriptors are employed, including a stability function, the HOMO-LUMO energy gap, and atomic radial distances of the atoms, as well as a similarity function. The results demonstrate that the structural motifs change from planar to shell-like structures with low-symmetry. In addition, the growth patterns of Ptn clusters also are analyzed using these descriptors, suggesting that meta-stable isomers also play a role in the growth process. Studying the impact of zero-point vibration and of temperature on the energetic properties of the different isomers, we found only very small effects, implying that properties found for T = 0 are relevant also at elevated temperatures. On the other hand, even though Pt is the neighbor to Au in the periodic table, the properties of Ptn clusters differ markedly from those of Aun clusters, and it can therefore be expected that the properties of AuPt nanoalloys will not resemble those of the pure clusters.