Study On The Structure And Property Of K-Cu And Na-Hg By First-Principles Calculations

The elements potassium and copper are immiscible under environmental conditions.Stress can significantly change the electronic structure of an element,thus facilitating interactions between different elements.Four new K-Cu compounds(K₃Cu₂,K₂Cu,K₅Cu₂,and K₃Cu)were predicted to exist stablly at 10-50 GPa by global structure search and first-principles calculations.In particular,the X-ray diffraction pattern of K₃Cu₂ is highly consistent with that of the K-Cu compound synthesized by Snider and Badding.In the different structures of K-Cu compounds,Cu atoms show different aggregation patterns,including linear chain,double chain,dimer,and isolated copper anion.The analysis of the electronic structure shows that Cu atoms accept the electrons of K atoms and exist in the six-membered lattice of K as anions.The 4s orbitals are completely filled and the 4p orbitals are partially filled,showing properties similar to those of the elements in the p region.The covalent interactions between Cu and Cu atoms with sp and sp² hybridization are observed.These results provide ideas for understanding the facies diversity of alkali/alkaline earth metal-precious metal systems.The transition metal Hg element has 5d¹⁰6s² electron shell,which can be changed into cations by oxidation(losing electrons).In mercury compounds,its negative oxidation states are uncommon.We combined particle swarm optimization algorithm and evolutionary algorithm to systematically study the structure,electronic structure and chemical bond characteristics of sodium amalgam compounds under normal pressure and high pressure.We have predicted six new Na-Hg stoichiometrics(Na Hg₃,Na Hg₄,Na₂Hg,Na₄Hg,Na₅Hg,and Na₆Hg).The structure of the mercury-rich components is characterized by the accumulation of Na Hg_n(n=6,8,10,12)polyhedra with sodium atoms as the center.Electronic structure analysis showed that Hg-Hg covalent interactions related to sp hybridization were found in these compounds.The structure of the sodium-rich components is presented by the accumulation of sodium polyhedra with mercury atoms as the center.The electron structure analysis showed that the mercury atom could acquire electrons from the sodium atom and occupy the Hg-6p orbital.In particular,in C2/m-I-Na₄Hg,part of the charge is concentrated in the sodium octahedron in the form of electron anions,with a central charge density of more than 0.6 e V/bohr³,showing the characteristics of a zero-dimensional electron compound.