Microscopic Mechanism of Stereochemically Active Lone Pair Studied from Orbital Selective External Potential Calculation

TL;DR

This paper uses a novel orbital selective external potential (OSEP) method to elucidate the microscopic origin of stereochemically active lone pairs, revealing the importance of cation s-p orbital mixing and structural effects in certain compounds.

Contribution

It introduces the OSEP method to study lone pairs, demonstrating the role of s-p orbital mixing and structural influences in their formation and stability.

Findings

On-site s-p orbital mixing is crucial for lone pair formation.

Structural variations significantly affect lone pair presence.

Lone pair formation can lead to structural instabilities in specific compounds.

Abstract

The nature of the stereochemically active lone pair has long been in debate. Here, by application of our recently developed orbital selective external potential (OSEP) method, we have studied the microscopic mechanism of stereochemically active lone pairs in various compounds. The OSEP method allows us to shift the energy level of specific atomic orbital, therefore is helpful to identify unambiguously the role of this orbital to the chemical and physical properties of the system we are interested in. Our numerical results, with compelling proofs, demonstrate that the on-site mixing of cation valence s orbital with the nominally empty p orbitals of the same subshell is crucial to the formation of lone pair, whereas the anion p orbital has only small effect. Our detailed investigation of Sn and Pb monochalcogenides show that structures of these systems have significant effects on lone pairs. In return, the formation of lone pair, which can be controlled by our OSEP method, could result in structural instabilities of Sn and Pb monochalcogenides.