Theoretical Studies On The Crystal Structures And Properties Of Iodine-fluoride Compounds Under High Pressure

The VIIA family elements in the periodic table,that is the halogen family elements,can form halogen compounds,also called interhalogen compounds.Previous studies for halogen compounds have mainly focused on their properties at ambient pressure.The particle swarm-optimized crystal structure analysis method(CALYPSO)was not used until 2019 to predict the structure of iodine and fluorine hybrids under high pressure,however,the structure of iodine monofluoride(IF)under high pressure was not determined.Compared with ambient pressure,under high pressure,the distance of interatomic in material can be changed,which the charge between atoms can be redistributed and the crystal structure can be changed to form a new phase of high pressure,so that the material that the structure phases transitions occur and the physical properties may also be changed and may not have the behavior at ambient pressure,which provides us with a new way to further understand the properties of materials,explain the appearance of ambient pressure,and provides probability to the discovery of new appearance,new laws,the development of new theories.In this paper,the high-pressure structures and properties of IF,a halogen complex formed by iodine and fluorine,were studied.First,in this paper,the high pressure crystal structures of fluorine and IF compound are predicted by using the unbiased CALYPSO(Crystal structure AnaLYsis by Particle Swarm Optimization)structure prediction method combined with first-principles calculations to find its ground state or metastable state structures.The predicted structures were optimized by using VASP.Thus,the phase transition sequence of fluorine under high pressure is C2/c?Cmca?Immm?I4/mmm;the phase transition sequence of IF under high pressure is P1?P21c-I?P21/c-??I4/mmm,and the phase transition pressures are 3 GPa,16.5 GPa and 46 GPa,respectively.Secondly,the properties(include elastic constants,phonon dispersion curves,electronic band structures and partial density of state and electronic local functions)of IF compound under high pressure were calculated using VASP.These results of the calculation indicate that the P1 structure under ambient pressure is metastable state,but other structures are dynamically stable in the range of pressure where their energy is stable.The P1 and P21/c-I structures are non-metal phases,and the P21/c-? and I4/mmm structures are metal phases.Our study of the high pressure phases of IF halogen compound will provide fundamental insights for further exploration the structural phase transitions of other halogen compounds under high pressure conditions.