Particle Swarm Optimization Investigation Of Stable Structures Of Pt-Pd-Au Alloy Nanoparticles

Owing to high stability and high specific surface area, platinum group alloy nanoparticles show superior catalytic performance compared with signal crystal nanoparticles. Since structure determines catalytic performance of nanoparticles, a further research of the stable structure of nanoparticles is of great importance to understand the catalytic activity. At present, it is difficult to obtain the precise atomic distribution of the stable structure of nanoparticles only by using the chemical experiment method. The results calculated by the potential function and computer simulation are somehow suit for analyzing the atomic distribution from the perspective of atoms.In this paper, we mainly focus on the research of Pt-Pd-Au alloy nanoparticles. The quantum Sutton-Chen many-body potentials are employed to describe the interaction between atoms. To optimize the potential energy of alloy nanoparticles, we firstly build a optimization model of alloy nanoparticles, then we apply an improved particle swarm optimization algorithm, which bring in an exchange operation, to solve the optimization model. Further, the structural stability of THH alloy nanoparticles (including Pt-Pd-Au trimetallic nanoparticles and Pt-Pd, Pt-Au, Pd-Au bimetallic nanoparticles) with fixed size and atomic proportion are investigated.To verify the effectiveness of the proposed algorithm, the stable structures of Pt-Pd-Au alloy nanoparticles with443,1417, and3285atoms are studied at the atomic proportion of Pt:Pd:Au=0.5:0.25:0.25, and the comparative analysis between the proposed improved algorithm and traditional algorithm are also provided. Moreover, independent experiments are performed to verify the stability of the proposed algorithm. The experimental results show that the proposed algorithm is effective and stable for searching the stable structure of alloy nanoparticles.By analyzing the atomic distribution of stable structure, we can draw the following conclusions:1) Pd atoms (in Pt-Pd alloy nanoparticles) and Au atoms (in Pt-Au alloy nanoparticles) tend to distribute in the outer layers, yet the Pt atoms tend to distribute in the inner layers;2) the distribution of Pd atoms and Au atoms in Pd-Au alloy nanoparticles are affected by size and atomic proportion. Specifically, with lower Pd proportion, Au atoms tend to distribute in the outer layers, yet the Pd atoms tend to distribute in the inner layers; With higher Pd proportion, the two different atoms show a competitive relationship in the outer layers;3) the atomic distribution of Pt-Pd-Au trimetallic nanoparticles coincides with the results of the bimetallic nanoparticles;4) the more orderly the atomic distribution is, the lower the potential energy of the alloy NPs is, and ultimately the more stable the structure is.