Can HHe+ exist at high pressure: Exploration of high pressure induced HF–He compounds

HHe+ is considered as the strongest acid and most powerful proton donor known to human. Whether HHe+ exists at planetary high pressure environment is a quite important problem in physics, chemistry and planetary sciences. Here, using the ab initio evolutionary algorithm USPEX package, we searched HF–He system, which was reported as the most possible candidate to contain HHe+. The calculation proved HHe+ cannot form at pressure <1000 ​GPa, due to a conflict between the covalent component in symmetric hydrogen bond and ionic HHe+. Although He atoms have no chemical bonding with other elements, they can supply a chemical pressure, leading to two new phases He2(HF)4 and He(HF). With coplanar (HF)4 rings, He2(HF)4 have an aromaticity-like electronic behavior while He(HF) has a new type of chiral HF chain. The formation of He2(HF)4 and He(HF) prove that the chemical pressure from He, on par with external pressure, have ability to control the structural and electronic configuration and induce some new familiars of compounds include H and He elements which are fundamental planetary materials in giant planets.