Ab Initio High Pressure Investigations of InI

Abstract

AbstractThe high pressure behaviour of InI is studied by DFT‐calculations and compared with experimental data. The existence of a 5s2 electron pair in In+ represents an unfavourable bonding situation for high symmetry structures because of effective closed shell repulsion. Since cations with a ns2 electron pair are highly polarizable and the electronic situation is more favourable in the low symmetry structure InI prefers a TlI‐type structure at ambient pressure. A pressure induced transition to the more densely packed high symmetry CsCl‐type structure takes place at about 19 GPa according to our calculations.At ambient pressure the interactions are predominantly ionic. However with increasing pressure the distances between In+ cations in the TlI‐type structure diminish drastically, mainly due to the changing space requirement of the lone electron pair. Apart from ionic interactions further bonding interactions between the In+ cations occur. At elevated pressure the electron localization function (ELF) as well as the band structure diagrams suggest metallic bonding between the In+ within the zigzag chain, i. e. increasing bonding interactions between the In+ cations due to the electron pair and its s‐p‐mixing. At ambient pressure In‐In interactions are rather weak and the space requirement of the lone electron pair mainly determines the characteristic arrangement of the ions. At elevated pressure the In‐In interactions become stronger and stabilise themselves additionally the specific structural arrangement.