Study On The Physical Properties Of Organic Compound Materials Under High Pressure

The article presents an in-depth investigation of the molecular structure,electronic properties,mechanical characteristics,and optical properties of three crystals,4-guanidino benzene sulfonamide（C₆H₉N₃O₂S）,nickel dichloride tetrasulfide（Ni Cl₂-4SC（NH₂）₂）,and cobalt（II）acetate（Co（HOCH₂CO₂）₂）,under different pressure conditions,using density functional theory（DFT）simulations based on first-principles.The results show that the C₆H₉N₃O₂S crystal structure exhibits distortion and anisotropy of lattice constants at pressures of 70 GPa and 270 GPa.The electronic properties indicate a semiconductor-metal-semiconductor phase transition,which implies that pressure can sensitively modulate the electronic structure.At 0 GPa,the real part of the dielectric constant exhibits metal reflection characteristics within the energy range of 15.6-20.2 e V,indicating no light propagation.At 270 GPa,the imaginary part of the dielectric constant has a non-zero static electric field,confirming the metallic character of the electronic structure,and the real part of conductivity shows a peak increase of 223%,indicating the instability of the crystal structure.For the Ni Cl₂-4SC（NH₂）₂ crystal,an increase in pressure within the range of 0-60 GPa leads to increased polarization,making the crystal more sensitive to external electric fields.Pressure-induced changes in the lattice structure and electronic structure cause an increase of 100%in the low-energy peak optical activity of the reflection spectrum,as well as changes in the molecular vibration modes and electronic transition states,which disrupt intermolecular interactions and eliminate the oscillations of the absorption spectral peak after 40 GPa.Similarly,at 40 GPa,the molecules in the crystal have higher energy,leading to the upward shift and increased amplitude of the energy loss function in the high-energy region and the downward shift of the energy loss function in the low-energy region.The Co（HOCH₂CO₂）₂ crystal shows structural distortion at 75 GPa,and the features of the bandgap and density of states reveal a semiconductor-near-metal phase transition,indicating that pressure can regulate both the electronic and crystal structures.Analysis of the differential charge density shows that increased pressure can affect the electron capture and release capability and form new covalent bonds.The elastic constants under pressure show that the new chemical bonds or molecular arrangements make the material more susceptible to plastic deformation in local areas.Compared to 70 GPa,the volume modulus,shear modulus,Young’s modulus,and Poisson’s ratio at80 GPa increase by 32.2%,16.4%,18.1%,and 5.6%,respectively,indicating that the crystal has better resistance to compression,shear,elastic deformation,and strain distribution properties,but the hardness decreases by 3.6%,and the material’s ability to resist permanent deformation weakens.Finally,an analysis of the change in electron occupancy with increasing pressure shows that the electron overlaps population values between relevant atoms increase by 38%and 642%at 70 GPa,indicating improved electrical conductivity.This study demonstrates that high-pressure conditions can effectively regulate the structure and properties of materials.The findings provide a basis for further research on developing new materials with desired properties under high-pressure conditions.