Introduction

Rare earth elements have many unique properties. Adding trace rare earth elements into metal materials can improve the microstructure, mechanical properties, oxidation resistance and corrosion resistance of metals to varying degrees. The results show that the addition of rare earth elements in the smelting process of metals can play a role in purifying, modifying inclusions and microalloying[1-6]. These effects will change the morphology and distribution of inclusions in metals, so that more inclusions with very small particle diameter and dispersed distribution are generated in the solidification process of metals, and then improve their comprehensive properties. At present, the mechanism of rare earth’s morphology and action form in metals is not clear, which affects its efficient utilization.As a transition state between solid state and gas state, the emergence of cluster research provides a suitable research method for the development and improvement of the theory of atomic bonding, the existence form and the formation law of various macromolecules.
Yttrium oxide (Y2O3) is a deoxidation product of rare earth treatment of molten steel. It is a typical rare earth oxide and has the general properties of rare earth oxides. It has a wide range of technical applications in the fields of electronics, optics, mechanical engineering, metallurgical engineering and catalyst support[7]. At room temperature, yttrium oxide has a C-type cubic structure of rare earth oxides, belonging to the body-centered cubic structure of iron manganese ore type (space group Ia3), similar to fluorite (CaF2) structure with a quarter anion vacancy, and the band gap is 5.8 eV[8-10]. Yttrium oxide cluster is a kind of transition state and intermediate product in the nucleation of yttrium oxide crystal. At present, most of these studies restricted to the small size with monomer, dioxide, and trioxide clusters[11-14]. In the experiment, Wu and Wang[15] studied the electronic structure of small YOn clusters with n=1−5 by photoelectron spectroscopy (PES), obtained the vibration-resolved photoelectron spectroscopy of YOn, and measured the electron affinity of YO. Pramann[16]et al. studied the electron affinity and vertical ionization energy of YnOm clusters with n=2−10, m=1−3, discussed the evolution process of the electronic structure of neutral yttrium oxide clusters, and compared the difference of yttrium oxide dissociation energy. Knickelbein[17] calculated the photoelectric energy spectra of Yn and YnO clusters with n=2−31, and studied the variation law of their vertical ionization energy. In terms of theoretical calculations, Amol B. Rahane[18]et al. studied small-sized yttrium oxide clusters with molecular number of 1-10, and discussed their stability and electronic characteristics. Rong Li and Qiyao Zhang[19, 20] studied the structure and stability of (Al2O3)n(n=7 and n=15), and obtained many isomers. Xiao Jianyun[21]et al. studied (HgSe)n(n=1-6) clusters using density functional theory, obtained the equilibrium geometry, vertical ionization energy results, and analyzed the atomic net charge distribution, frontier molecular orbital characteristics.
Previous studies only studied the structure and photoelectric energy spectrum of yttrium oxide ions or single element yttrium, and discussed the effects of different oxygen to metal ratios on their structure and electronic properties. However, there were few studies on the neutral Y2O3 clusters structure, especially the cluster structure with medium and large sizes. In this paper, the structure and properties of yttrium oxide clusters are studied by artificial bee colony algorithm combined with quantum chemical calculation, in order to improve the thermodynamic data of nano yttrium oxide clusters, and lay the foundation for exploring the nucleation process of rare earth inclusions in metal materials, and provide technical guidance for the process of adding rare earth yttrium in metal and the size control of inclusions.