First Principle Study Of Organic Materials Under High Pressure

Materials research is increasingly becoming the academic research hotspots,especially optical,electrical and magnetic functional materials based on organic molecule.Various organic optical materials with excellent properties have been developed and applied to electron devices.The van der Waals force between the molecules of organic materials is weak,so the stability problem has seriously restricted its development.Therefore,nature studies will help to understand its basic properties and find ways to improve its stability and photoelectric performance,targeting organic materials under high pressure.Due to the harsh conditions of studying organic materials under high pressure,the use of computer simulation of the properties has important research significance.This paper first introduces the development of organic molecular materials and the study of high pressure phase transition,especially the research progress of high-pressure phase transition,and then introduces the theoretical basis and calculation methods.In the third to fourth chapters,the paper studies the crystal structure,electronic properties and optical absorption of organic materials benzoic acid and 2,6-dimethyl-4-(diphenylmethylene)-2,5-cyclohexadienone(?-DDCD)under high pressure conditions.In the high pressure range of 0~300 GPa and 0~250 GPa,this paper finds that the above two materials have complicated changes,by analyzing the variation tendencies of the lattice constant,bond lengths and bond angles,based on the first principle.In the pressure range 0~280 GPa,repeated formations and disconnections of hydrogen bonds between benzoic acid atoms occur several times,and a new benzoic acid dimer at 100 GPa and 280 GPa.It can be seen that the b-direction is much stiffer than the other two axes in the structure of ?-DDCD,suggesting the anisotropy of the dimension.Then,by analyzing the bandgap and density of states,it is found that the structural transformations of the benzoic acid crystals are as follows: insulator?semiconductor?metal,in the pressure range 240 ~ 280 GPa.And in the pressure range 110~170 GPa,repeated transformations between metal and semiconductor occur four times,suggesting the structural instability of ?-DDCD in this pressure range.In addition,from the absorption spectra,it can be seen that both benzoic acid and ?-DDCD have the relatively high optical activity with increasing pressure.The results show that high pressure has an influence on the stability and photoelectric performance of benzoic acid and ?-DDCD,and has a certain reference value for the application of organic materials in electron devices.