First-principles study of K, Ni and P doped superconductor AFe₂As₂ (A=Ba, Sr)

The characteristics of structural changes, Fe magnetic moment and electron density of K, Ni and P-doped AFe₂As₂ (A = Ba, Sr) were studied by first-principles calculations. After the introduction of the dopants, the Fe–As bond length and As–Fe–As angle became smaller. Although K substitution involved hole doping, Ni substitution involved electron doping, and P substitution was isovalent doping, K, Ni and P doping makes Fe and As more closely related, and the electron density near As atoms were strengthened. After doping, the distribution tendency of electron density near the As ions leads to coupling constants J₁, J₂ decreases eventually, which mean AFM order is suppressed. This redistribution of electron density is the inducement of superconductivity.