Rubidium Polyhydrides Under Pressure: Emergence of the Linear H3− Species

Abstract The structures of compressed rubidium polyhydrides, RbH n with n >1, and their evolution under pressure are studied using density functional theory calculations. These phases, which start to stabilize at only P =2 GPa, consist of Rb + cations and one or more of the following species: H − anions, H 2 molecules, and molecules. The latter motif, the simplest example of a three‐center four‐electron bond, is found in the most stable structures, RbH 5 and RbH 3 , which metallize above 200 GPa. At the highest pressures studied, our evolutionary searches find an RbH 6 phase which contains polymeric ( ) ∞ chains that show signs of one‐dimensional liquid‐like behavior.