Conclusions

The initial configuration of Yttrium oxide clusters (Y2O3)n(n=1-15) was creatively constructed by combining artificial bee colony algorithm with density functional theory. The structures of large and medium-sized yttrium oxide clusters with molecular number greater than 10 were established for the first time, and their ground state structures were determined by structural optimization and frequency analysis in Gaussian 09 software package. The average binding energy, second-order difference energy, H-L energy gap,density of states and thermodynamic properties of each structure were calculated and analyzed in detail.the result shows:
  1. For small clusters with n<5, oxygen atoms and yttrium atoms tend to form cage-like clusters. With the increase of size (n=6-15), the clusters structure change from cage-like to space stair-like, and gradually evolves into stable ellipsoid-like structure.
  2. The stability and molecular orbital of the clusters were analyzed in detail, and it was found that the cluster structure was generally stable. Because the valence bond orbital of oxygen atom is less than half full (2P4), and the valence bond orbital of yttrium atom is full (5S2), the probability of electron filling p orbital is much larger than that of filling s orbital, so the binary mixed yttrium oxide clusters have more stable structures than the single yttrium clusters. When the number of cluster molecules n=2,4,7,9, the relative stability is higher, and the second-order energy difference score is basically consistent with the results of H-L energy gap in determining the stability of cluster structure. The major contribution from S basis function of oxygen (magenta curve) is due to low-lying MOs instead of frontier MOs. HOMO is almost purely contributed by yttrium orbitals.
  3. Cp, H and S of (Y2O3)n increased with the increase of T, and increased with the increase of cluster size. Gv decreases with the increase of temperature, and the change rule with cluster size is greatly affected by T. In the temperature range of 300K-500K, the Gv lines intersect each other, indicating that the stability of nanoclusters has changed in the temperature range of 300K-500K. The thermodynamic properties of (Y2O3)n vary greatly with the number of clusters, which is similar to the size effect of the thermodynamic properties of nanoscale materials.
The structure and related thermodynamic data of nanoclusters calculated in this study have certain guiding significance for studying the nucleation of yttrium oxide crystals from the perspective of nanothermodynamics.