Electronic structure of group IV tetramers (Si4–Pb4)

Abstract

Geometries and energy separations of ten electronic states of Ge4, Sn4, and Pb4 are computed and compared with Si4. We employ complete active space multiconfiguration self-consistent-field followed by multireference singles + doubles configuration interaction calculations. The ground states of Ge4–Pb4 are found to be 1Ag states with equilibrium geometries of rhombus similar to Si4. Relativistic effects are found to be significant for Pb4. Atomization/dissociation energies of Ge4–Pb4 are computed and compared with Si4. Pb4 was found to be considerably less bound compared to other tetramers. The energy separations of the excited electronic states were found to decrease, especially the splitting between the rhombus and tetrahedral structures, as one goes down the group.