Theoretical Study On Structures And Properties Of Rubidium Fluoride Compounds Under High Pressure

With the development of high pressure experimental techniques and first-principles crystal structure prediction methods,many unconventional compounds have been theoretically predicted and experimentally synthesized,and these compounds exhibit unique physical and chemical properties.First principles calculation method combined with random structure search method was used to systematically study the crystal structure electronic properties and chemical bond properties of the stable ratio Rb-F compound under high pressure.Several new Rb-F compounds were found and the following innovative research results were obtained:(1)In the pressure range of 0-300 GPa,we have predicted several new thermodynamically stable compounds,Rb F₂,Rb F₃,Rb F₄ and Rb F₅.In these compounds,homonuclear bonds of F₃,F₄ and F₅ are readily formed.Through ELF and COHP calculations,the bonding type of F-F bond was determined as covalent bond,and linear[F₃]^-species existed in R-3m-Rb F₃,nonlinear[F₃]^-species existed in Pnma-Rb F₃ and C2/m-Rb F₄,linear[F₄]^2-species existed in Pbam-Rb F₂,and in Pnma-Rb F₅,there exists a V-type symmetric[F₅]^-species.Electronic structure calculations show that,except for the metal Fd-3m structure of Rb F₂,all stable structures are insulators,and 5p orbital of F plays an important role at Fermi level.(2)Several new stable and metastable compounds,Rb F₂,Rb F₆,Rb F₇ and Rb F₈,have been predicted in the ultra-high pressure range of 1-5 TPa.Through bond length analysis of COHP and ELF calculation,it can be seen that p electrons in the inner layer of rubidium in these compounds are involved in bonding,forming Rb-F covalent bonds.The Bader charge analysis shows that the rubidium atoms present high oxidation states in compound Rb F_n(n=2-7),and oxidation states increases linearly with the number of F atoms.In addition,we also explored the superconductivity of Rb F₂,Rb F₆ and Rb F₇,and found that only Rb F₆ produced a superconducting transition temperature of about12.5 K at 3 TPa.