Stability of hypothetical AgIICl2 polymorphs under high pressure, revisited : a computational study

TL;DR

This computational study investigates the stability of hypothetical AgIICl2 polymorphs under high pressure, revealing their instability and limited synthesis prospects due to charge transfer and decomposition tendencies.

Contribution

It provides a comparative analysis of various computational methods on AgCl2 stability, highlighting the instability of all considered structures across pressure ranges.

Findings

All candidate structures have negative enthalpy of formation but are unstable towards decomposition.

Some AgIICl2 polymorphs are stable below 20 GPa in the SCAN approach.

High pressure promotes charge transfer and phase separation, destabilizing AgCl2.

Abstract

A comparative computational study of stability of candidate structures for an as yet unknown silver dichloride AgCl2 is presented. It is found that all considered candidates have a negative enthalpy of formation, but are unstable towards charge transfer and decomposition into silver(I) chloride and chlorine within the DFT and hybrid DFT approaches in the entire studied pressure range. Within SCAN approach, several of the true AgIICl2 polymorphs (i.e. containing Ag(II) species) exhibit a region of stability below ca. 20 GPa. However, their stability with respect to aforementioned decomposition decreases with pressure by account of all three DFT methods, which suggests a limited possibility of high pressure synthesis of AgCl2. Some common patterns in pressure induced structural transitions observed in the studied systems also emerge, which further testify to an instability of hypothetical AgCl2 towards charge transfer and phase separation.