A newly predicted stable calcium argon compound by ab initio calculations under high pressure

Abstract

High pressure can change the valence electron arrangement of the elements, and it can be as a new method for the emergence of unexpected new compounds. In this paper, the Ca–Ar compounds at 0–200 GPa are systematically investigated by using CALYPSO structure prediction methods combined with first principles calculations. The study of the Ca–Ar system can provide theoretical guidance for the exploration of new structures of inert elemental Ar compounds under high pressure. A stable structure: P63/mmc-CaAr and six metastable structures: Rm-CaAr2, P4/mmm-CaAr2, Pm1-CaAr3, P4/mmm-CaAr3, P21/m-CaAr4 and Pm1-CaAr5 were obtained. Our calculations show that the only stable phase P63/mmc-CaAr can be synthesized at high pressure of 90 GPa. All the structures are ionic compounds of metallic nature, and surprisingly all Ar atoms attract electrons and act as an oxidant under high pressure conditions. The calculation results of ab initio molecular dynamics show that P63/mmc-CaAr compound maintains significant thermodynamic stability at high temperatures up to 1000 K. The high-pressure structures and electronic behaviors of the Ca–Ar system are expected to expand the understanding of the high-pressure chemical reactivity of compounds containing inert elements, and provide important theoretical support for the search of novel anomalous alkaline-earth metal inert element compounds.