Structural And Electronic Properties Of "Cu₁3"^± Clusters Studied By Genetic Algorithm And Density Functional Theory

Clusters have special geometries and peculiar physical and chemical properties, and their potential applications cause widespread concern. Metallic copper clusters have great importance in catalysis, nanotechnology and large-scale integrated circuit manufacturing. Therefore, recent research on copper clusters has become a very popular area of study. In this research, we select the 13-atom copper cluster. In order to obtain the lowest energy structure of the 13-atom copper cluster, first we use genetic algorithm and Gupta many-body potential to study the geometrical properties of Cu₁₃ cluster, and a large number of low-energy structures are obtained. Then by using the first principles density functional theory (DFT) calculations (the DMOL software) the initial structures are further optimized in order to get the low energy structures in DFT level. We use DMOL software to calculate the average binding energy, HOMO-LUMO gap, ionization energy and electron affinity, and other physical properties of Cu₁₃ cluster.We summarize our main conclusions as follows:1. Although binding energy order of Cu₁₃ clusters calculated by a genetic algorithm and first principle calculation results are not the same, but the genetic algorithm provides a large number of candidate structures, and the obtained structures are re-optimized by density-functional theory (DFT) calculations can still be effective (and efficient) to find the true ground state of Cu₁₃ cluster geometry, and also providing more low-excited states geometry. We believe that genetic algorithm (combination of first-principles calculations) can still offer the efficiency of structure optimization in dealing with a system with non-compact low symmetric ground-state geometry.2. Through DFT investigations on the neutral and charged Cu₁₃ clusters we find: (1) The lowest energy structures of neutral and charged Cu₁₃ clusters are not the same; (2) For the 13-atom Cu cluster, the high-symmetric structures are substantially not favorable; (3) Stability of the low energy structures of Cu₁₃ cluster can be enhanced by charging; (4) The magnetic moments are minimized for the lowest energy structures of neutral and charged Cu₁₃ clusters, that means the total magnetic moment would be 0μB with even number of total electrons and would be 1μB with even number of total electrons, and as a result there is no spin splitting for the neutral and charged Cu₁₃ clusters in their ground-state; (5) The calculated ionization potential and electron affinity are in agreement with the experimental observations.