Study On The Structure And Physical Properties Of Organic Materials Under High Pressure

With the wide application of semiconductor materials,the application requirements in extreme environments such as high temperature and high pressure are increasing and the requirements for the preparation of semiconductor materials are also getting higher and higher.Traditional experimental method requires relatively harsh experimental conditions and is not suitable for the study of material properties in extreme environments.In this paper,the first-principles based on density functional theory are used to carry out comprehensive computational simulation analysis on the structure of materials,which makes the research of materials more directional and practical.The molecular and electronic structures and optical properties of tetrahydro crystal,2-（acetoxy）benzoic acid crystal and 3-Phenyl crystal in the pressure range of 0-300GPa are calculated and analyzed by computational simulation.The main research contents are as follows:（1）Firstly,it is found that the lattice constant,bond length and bond angle of tetrahydro crystal have obvious mutations at 70,90,170 and 240GPa.The results of band gap and density of states of tetrahydro crystal show that the electronic structure of tetrahydro crystal is relatively stable in the pressure range of 0-160GPa.When pressure continues to increase to 280GPa,tetrahydro crystal change from semiconducting phase to insulating phase.Finally,the optical properties of tetrahydro crystal are compared and analyzed under different pressures,the absorption coefficient has four absorption peaks at 170GPa.The calculation of complex dielectric function shows that tetrahydro crystal has anisotropy.Refractive index n₀increases from 1.49 of 0GPa to 3.37 of 190GPa,the peak of the reflectance spectrum is doubled.Conductivity and loss function move to the high energy region.（2）2-（acetoxy）benzoic acid crystal appeares bonding process at 80 and 90GPa.Band gap and density of states of the crystal show that the crystal is semiconducting phase at 80GPa and transforms into metal phase at 270GPa.Finally,the optical properties of the crystal are compared and analyzed,absorption coefficient at 270GPa change from a sharp peak to two interconnected peaks from the strongest peak.Refractive index n₀increased from 1.61 at 0GPa to 5.3 at 270GPa.Reflectance spectrum peaks appear multiplied and move toward the high-energy region.Conductivity and loss function peaks appear blue-shifted.（3）The lattice constants,bond lengths and bond angles of 3-Phenyl crystal change gently from0 to 160GPa and change more drastically after 170GPa.Through the analysis of the band gap and density of states of the 3-Phenyl crystal,the band gap of the crystal decreases rapidly at 90GPa shows a semiconducting phase,which transforms into an insulating phase at 240GPa.The optical properties of 3-Phenyl crystal are compared and analyzed,and it is found that the absorption coefficient changed significantly between 180 and 240GPa.Refractive index n₀increases from 1.73at 0GPa to 3.19 at 90GPa and the peak of the reflection spectrum increases slightly.Conductivity increases twice and the loss function showed a loss peak at 32.7e V.By studying the crystal structures,electronic structures and optical properties of organic materials tetrahydro crystal,2-（acetoxy）benzoic acid crystal and 3-Phenyl crystal under high pressure,it is demonstrated that extreme conditions can effectively control the structure and optical properties of materials.It provides a new idea for further research on the properties of organic materials in the future.