First-principles Study Of Two-dimensional Al-Ni-Co Quasi-unit-cell Clusters

Al-Ni-Co quasicrystals are one kind of two-dimensional quasicrystals,many scholars have studied their structures.However,their electronic properties and density of states are less studied.In order to explore the relationship between their structure and electronic properties,based on the experimental results of high resolution Z-contrast imaging of transmission electron microscopy,a quasi-unit-cell model of b-Ni phase and 5f phase of Al-Ni-Co quasicrystals was constructed,and its ground state energy,electronic properties,density of states was studied using first-principles calculations,the calculation results of different transition metal element?TM?atomic ratio models were compared and analyzed.The conclusions are as follows:1.Based on the density functional theory,the 10 f NinCo40-n?n=0⁴0?quasi-unit-cell models of Al-Ni-Co decagonal quasicrystal b-Ni structure were studied.After the geometry optimization of the six structures with n = 0,8,16,24,32,40,the inner ring atoms were all contracted inwards.The diameter of the middle ring in the optimized structure is 13.0 ?,and the diameter of the inner ring is 4.3 ?.By analyzing the relationship between the structure and energy of these quasi-monocyte clusters,it was found that the excess energy increases significantly when WNi>50%.And Co is biased to occupy the middle ring,the excess energy of the quasi-unit-cell cluster decreases with the increase of Co ratio in the middle ring.The density of state analysis shows that there is a pseudo-gap near the Fermi surface,and the structure of the Co atoms occupying the outer ring has a higher TDOS curve than that of the structure where the Co atoms occupy the inner ring.2.Based on the density functional theory,the 5f₁ NinCo40-n?n=0⁴0?quasi-unit-cell models of the Al-Ni-Co decagonal quasicrystal 5f structure were studied.For n = 0,8,16,24,32,40,the geometry optimization of these six structures showed they are symmetrically broken.Based on the 5f₁ model,the 5f₂ model was constructed,and was also optimized geometrically.It was found that the inner ring atom position contracted inwards,and it still keeps five-fold rotation symmetry.The circumcircle diameter of the middle ring is 12.7 ?,and the circumcircle diameter of the inner ring is 4.3 ?.By analyzing the relationship between the structure and energy of the 5f₂ model,it was found that Ni is biased toward the outer ring,and the excess energy increases sharply when WNi>50%.As the proportion of Ni atoms in the outer ring increases,the excess energy of the cluster increases.