The Pseudo Jahn-Teller effect and NBO analysis for untangling the symmetry breaking in the planar configurations of M 2 X 4 + (M=Si, Ge and X=Cl, Br, I): effect on electronic structure and chemical properties

Abstract

Abstract The Pseudo Jahn- Teller effect is a significant tool for evaluating molecular distortion and symmetry breaking. The PJT effect associated with NBO analysis can be a powerful method for studying the structural properties variations arising from D2h → C2h distortions. Ab initio calculations have shown that C2h non- planar structures are more stable than planar structures with D2h symmetry. The \(({B}_{3u}+{B}_{1u})⨂{b}_{2g}\) PJTE problem of M2X4+ compounds is a result of the coupling between the ground B3u state and the exited B1u state in the Qb2g direction causes. Also, the difference in M and X atoms can affect the PJT instability of compounds. The findings of this work showed that the energy gap between the ground and excited states that have D2h symmetry decreases from M2Cl4+ to M2I4+ and increases from Si2X4+ to Ge2X4+. In fact, there is a significant relationship between instability of high-symmetry configurations, geometric parameters, electron delocalization, chemical hardness, electronegativity, and PJT stabilization energies. These results may serve to evaluate the distortion of similar systems.