ZnxMg60–xO60 Nanoclusters with Tunable Near-Ultraviolet Energy Gaps

Abstract

(MgO)60 and (ZnO)60 are predicted to be magic-number clusters in the shapes of cuboid (CB) and double-layer cage (DC), respectively. The composite ZnxMg60–xO60 nanoclusters that are isovalent to (MgO)60 and (ZnO)60 are studied using a basin hopping method with our newly developed combinatorial-ion-exchange (CIE) sampling technique and molecular dynamics in conjunction with density functional theory. The most stable ZnxMg60–xO60 is found to be either a CB (at low x) or a DC (at high x) nanocluster depending on the value of x with the crossover point at x = 42 or at Zn/Mg ≈ 2:1. CIE basin hopping calculations reveal that Zn prefers sites with the lowest Zn–O coordination, whereas Mg prefers sites with the highest Mg–O coordination. Aggregation of two small nanoclusters to form a large magic-number ZnO–MgO composite nanocluster is thermodynamically favorable. Born–Oppenheimer molecular dynamics simulations show that the aggregation is dependent on the structural motifs of the small (MgO)n and (ZnO)n reactant...