How to Identify Lone Pairs, Van der Waals Gaps, and Metavalent Bonding Using Charge and Pair Density Methods: From Elemental Chalcogens to Lead Chalcogenides and Phase‐Change Materials

Lone pairs explain the structure of many molecular solids, as well chain-like or layered structures encountered in chalcogenide crystals. Such chalcogenides have enabled a plethora applications, including phase-change memories, thermoelectrics, topological insulators photoconductors. In these, lone also are invoked to unconventional material properties. The presence so-called van der Waals gaps and their low thermal conductivity been linked pairs. However, for some these systems, second view bonding has proposed, where atoms held together across interlayer spacing by shared electrons. To clarify this situation, herein, several systems which frequently emphasized reinvestigated theoretically. By comparing charge electron localization analysis terms Hartree–Fock-like pair density obtained from Kohn–Sham functional theory (KS-DFT), it is verified that governed pairs, whereas others not. As an example, crystalline Se demonstrated form with two covalent bonds pair, metavalenty essential characteristics Sb, Te being intermediate case.