Structural, electronic and vibrational properties of indium oxide clusters

Geometric, electronic and vibrational properties of the most stable and energetically favourable configurations of indium oxide clusters In_mO_n (1 ≤ m, n ≤ 4) are investigated using density functional theory. The lowest energy geometries prefer the planar arrangement of the constituent atoms with a trend to maximize the number of ionic In—O bonds. Due to the charge transfer from In to O atoms, the electrostatic repulsion occurs between the atoms with the same kind of charge. The minimization of electrostatic repulsion and the maximization of In—O bond number compete between each other and determine the location of the isometric total energy. The most stable linear In—O-In—O structure of In₂O₂ cluster is attributed to the reduced electrostatic repulsive energy at the expense of In—O bond number, while the lowest energy rhombus-like structure of In₂O₃ cluster reflects the maximized number of In—O bonds. Furthermore, the vibrational frequencies of the lowest energy clusters are calculated and compared with the available experimental results. The energy gap and the charge density distribution for clusters with varying oxygen/indium ratio are also discussed.