Electronic structure of the III–V tetramer clusters and their positive ions

Abstract

We study mixed group III–V tetramers and their positive ions, in particular, Al2P2, Ga2As2, In2Sb2, Tl2Bi2, and their positive ions. We employ ab initio complete active space multiconfiguration self-consistent field followed by multireference singles + doubles configuration interaction (MRSDCI) calculations. We also include the effects of spin–orbit coupling for Tl2Bi2 and In2Sb2 tetramers. The mixed III–V diatomics (AlP–TlBi) are also studied for comparison. Among the states and geometries considered here, we find that the lowest states of all four tetramers are 1Ag with rhombus equilibrium geometries. We considered several excited states of the positive ions and found that the 2B1u state with a rhombus geometry is the lowest for the positive ions. The binding energies and adiabatic ionization energies of all four tetramers are computed at the MRSDCI level and periodic trends are obtained. The Tl2Bi2 tetramer and TlBi dimer differ from their lighter analogs due to relativistic effects. We find that the binding energies per atom for the tetramers are larger than the trimers but comparable to the dimers.