Instability in pyramidal–tetrahedral structure including elements from group 14 induced by pseudo-Jahn–Teller effect

Abstract

The pseudo-Jahn–Teller effect (PJTE) of the pyramidal–tetrahedral A42− (A = C, Si, Ge, Sn) dianion analogues is investigated by quantum chemical calculations. The adiabatic potential energy surface cross sections obtained from ab initio calculation of the A42− analogues show instability for a degenerate E ground state. Thus, symmetry breaking phenomena induced by the PJTE occur in the series, and the unstable pyramidal–tetrahedral configuration with Td symmetry distorts to the equilibrium geometry structure (lower C2 symmetry) in all considered dianions. Additionally, the (E(1) + A1 + E(2)) ⊗ e problem is formulated for the analogues with the APES cross sections used in order to estimate the coupling constants by fitting the energies acquired from the PJTE equations. To restore the pyramidal–tetrahedral structure with Td symmetry and quenching the PJTE in the series, the PJTE in A42− analogues was suppressed through (1) adding two electrons to the A42− series and (2) either doping the A42− analogues with an atom from group 14 or trapping He2+ and Ne2+ inside the Si42− cage.