Structures, Energies, and Electronic Properties of Low-Index Surfaces of ??-Ni₃Nb: A First-Principles Calculations

First-principles calculations are carried out to study the surface structure, energies, and electronic properties of Ni3Nb(100), Ni3Nb(001), and Ni3Nb(110) based on the density functional theory (DFT). The surface relaxation results reveal that the relaxations are mainly localized in the first and second atomic layer, and Ni3Nb(110)-Ni experiences the largest surface relaxation (-16.95%), whereas Ni3Nb(001)-NiNb undergoes smallest relaxations. The surface energies of nonstoichiometric surfaces present a linear relationship with the chemical potential of Ni (Delta mu(Ni)), while those of stoichiometric surface are independent of Delta mu(Ni). Furthermore, Ni3Nb(001)-Ni and Ni3Nb(001)-NiNb are the most stable surfaces owing to their having the lowest surface energy in a wide range of Delta mu(Ni), while the nonstoichiometric Ni3Nb(110)-Ni and Ni3Nb(110)-NiNb surfaces with the largest surface energies are the most unstable surfaces. The electronic structures of nonstoichiometric surfaces are different from that of the bulk Ni3Nb, whereas the effect of surface relaxation on the electronic properties of the stoichiometric surface is weak.