First-principles Calculations on Structural Stability and Electronic Properties of the Strontium-Argon System at High Pressure

In order to explore the mechanism behind the stability of noble gas (NG) element compounds and make a systematic theoretical predictions for alkaline earth metal NG elements compounds, this paper focuses on the reaction of NG elements with alkaline earth metals. An in-depth theoretical predictions of the Sr-Ar system has been carried out by using the structure prediction method CALYPSO, to search for possible stable structures at different pressures. The structure optimizations and property analyses have been performed by first-principles calculation VASP code. We have discovered two hitherto unknown structures: the structure of Cmcm-SrAr and I4/mmm-SrAr3. The Cmcm-SrAr is stable in the pressure range of 150–210 GPa, while the I4/mmm-SrAr3 is stable in the pressure range of 190–300 GPa. Additionally, two metastable structures have been discovered under ultra-high pressure (UHP) conditions: P63/mmc-SrAr and P21/m-SrAr4. The analysis of the electronic band structure and density of states (DOS) of the four Sr-Ar compounds reveals that they all exhibit metallicity and are mainly contributed by the Sr-d orbitals near the Fermi level, which plays a crucial role in maintaining the stability of the crystals. In this paper, the superconducting properties of Sr-Ar structures are investigated for the first time, and it is found that these compounds are superconducting. The research findings will substantially enhance our understanding of the structural evolution in NG element compounds under high pressure.